tag:theconversation.com,2011:/us/topics/atom-970/articlesAtom – The Conversation2023-10-17T16:42:46Ztag:theconversation.com,2011:article/2113022023-10-17T16:42:46Z2023-10-17T16:42:46ZOnly 1% of chemical compounds have been discovered – here’s how we search for others that could change the world<figure><img src="https://images.theconversation.com/files/553049/original/file-20231010-21-ljmz9o.jpg?ixlib=rb-1.1.0&rect=49%2C74%2C5450%2C3586&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/chemical-tube-reaction-formula-light-598653854">Garsya/Shutterstock</a></span></figcaption></figure><p>The universe is flooded with billions of chemicals, each a tiny pinprick of potential. And we’ve only identified <a href="https://www.eurekalert.org/news-releases/993593">1% of them</a>. Scientists believe undiscovered chemical compounds could <a href="https://www.sciencedaily.com/releases/2021/08/210813100255.htm">help remove greenhouse gases</a>, or trigger a medical breakthrough much like penicillin did. </p>
<p>But let’s just get this out there first: it’s not that chemists aren’t curious. Since Russian chemist <a href="https://www.britannica.com/biography/Dmitri-Mendeleev">Dmitri Mendeleev</a> invented the <a href="https://www.britannica.com/science/periodic-table">periodic table of elements</a> in 1869, which is basically a chemist’s box of Lego, scientists have been discovering the chemicals that helped define the modern world. We needed nuclear fusion (firing atoms at each other at the speed of light) to make the last handful of elements. Element 117, <a href="https://www.rsc.org/periodic-table/element/117/tennessine">tennessine</a>, was synthesised in 2010 in this way. </p>
<p>But to understand the full scale of the chemical universe, you need to understand <a href="https://www.britannica.com/science/chemical-compound">chemical compounds</a> too. Some occur naturally – water, of course, is made of hydrogen and oxygen. Others, such as <a href="https://www.britannica.com/science/nylon">nylon</a>, were discovered in lab experiments and are manufactured in factories. </p>
<p><a href="https://www.bbc.co.uk/bitesize/topics/zstp34j/articles/zc86m39#:%7E:text=An%20element%20is%20a%20pure,There%20are%20118%20different%20elements.">Elements are made of one type of atom</a>, and <a href="https://www.livescience.com/37206-atom-definition.html">atoms are made of even tinier particles</a> including electrons and protons. All chemical compounds are made of two or more atoms. Although it’s possible there are undiscovered elements left to find, <a href="https://www.chemistryworld.com/news/beyond-element-118-the-next-row-of-the-periodic-table/9400.article">it’s unlikely</a>. So, how many <a href="https://www.wordnik.com/words/chemical%20compound">chemical compounds</a> can we make with the 118 different sorts of element Lego blocks we currently know?</p>
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<h2>Big numbers</h2>
<p>We can start by making all the <a href="https://www.britannica.com/science/diatomic-molecule">two-atom compounds</a>. There are lots of these: N<sub>2</sub> (nitrogen) and O<sub>2</sub> (oxygen) together make up 99% of our air. It would probably take a chemist about a year to make one compound and there are 6,903 two-atom compounds in theory. So that’s a village of chemists working a year just to make every possible two-atom compound. </p>
<p>There about 1.6 million three-atom compounds like H₂0 (water) and C0₂ (carbon dioxide), which is the population of Birmingham and Edinburgh combined. Once we reach four- and five-atom compounds, we would need everyone on Earth to make three compounds each. And to make <a href="https://sciencenotes.org/how-many-atoms-are-in-the-world/">all these chemical compounds</a>, we’d also need to recycle all the materials in the universe several times over. </p>
<p>But this is a simplification, of course. Things such as the structure of a compound and its stability can make it more complex and difficult to make.</p>
<p>The biggest chemical compound that has been made so far was <a href="https://pubs.acs.org/doi/full/10.1021/om900079y">made in 2009</a> and has nearly 3 million atoms. We’re not sure what it does yet, but <a href="https://doi.org/10.1039/C9TB02289A">similar compounds</a> are used to protect cancer drugs in the body until they get to the right place.</p>
<p>But wait, chemistry has rules! </p>
<h2>Surely not all those compounds are possible?</h2>
<p>It’s true there are rules – but they are kind of bendy, which creates more possibilities for chemical compounds. </p>
<p>Even the solitary “<a href="https://en.wikipedia.org/wiki/Noble_gas">noble gases</a>” (including neon, argon and xenon and helium), which tend to not bind with anything, <a href="https://www.aanda.org/articles/aa/abs/2014/06/aa23727-14/aa23727-14.html">sometimes form compounds</a>. Argon hydride, ArH<sup>+</sup> does not exist naturally on Earth but has been found in space. Scientists have been able to make synthetic versions in laboratories that replicate deep space conditions. So, if you include extreme environments in your calculations, the number of possible compounds increases. </p>
<p>Carbon normally likes being attached to between one and four other atoms, but very occasionally, for short periods of time, <a href="https://en.wikipedia.org/wiki/Methanium">five is possible</a>. Imagine a bus with a maximum capacity of four. The bus is at the stop, and people are getting on and off; while people are moving, briefly, you can have more than four people actually on the bus.</p>
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<a href="https://theconversation.com/confessions-of-a-chemist-i-make-molecules-that-shouldnt-exist-53326">Confessions of a chemist: I make molecules that shouldn't exist</a>
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<p>Some chemists spend their entire careers trying to make compounds that, according to the chemistry rulebook, shouldn’t exist. Sometimes they are successful.</p>
<p>Another question scientists have to grapple with is whether the compound they want can only exist in space or extreme environments – think of the immense heat and pressure found at <a href="https://oceanservice.noaa.gov/facts/vents.html">hydrothermal vents</a>, which are like geysers but on the ocean floor. </p>
<h2>How scientists search for new compounds</h2>
<p>Often the answer is to search for compounds that are related to ones that are already known. There are two main ways to do this. One is taking a known compound and changing it a bit – by adding, deleting or swapping some atoms. Another is taking a known chemical reaction and using new starting materials. This is when the method of creation is the same but the products may be quite different. Both of these methods are ways of searching for <em>known unknowns</em>. </p>
<p>Coming back to Lego, it’s like making a house, then a slightly different house, or buying new bricks and adding a second storey. A lot of chemists <a href="https://en.wikipedia.org/wiki/Mary_Elliott_Hill">spend their careers</a> exploring one of these chemical houses.</p>
<p>But how would we search for truly new chemistry – that is, <em>unknown unknowns</em>? </p>
<p>One way chemists learn about new compounds is to look at the natural world. Penicillin was found this way in 1928, when Alexander Fleming observed that mould in his petri dishes <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520913/">prevented the growth of bacteria</a>.</p>
<p>Over a decade later, in 1939, <a href="https://www.nobelprize.org/prizes/medicine/1945/florey/biographical/">Howard Florey</a> worked out how to grow penicillin in useful amounts, still using mould. But it took even longer, until 1945, for <a href="https://www.nobelprize.org/prizes/chemistry/1964/hodgkin/biographical/">Dorothy Crowfoot Hodgkin</a> to identify penicillin’s chemical structure. </p>
<p>That’s important because part of penicillin’s structure contains atoms arranged in a square, which is an unusual chemical arrangement that few chemists would guess, and is difficult to make. Understanding penicillin’s structure meant we knew what it looked like and could search for its chemical cousins. If you’re allergic to penicillin and have needed an alternative antibiotic, you have Crowfoot Hodgkin to thank. </p>
<p>Nowadays, it’s a lot easier to determine the structure of new compounds. The X-ray technique that Crowfoot Hodgkin invented on her way to identifying penicillin’s structure is still used worldwide to study compounds. And the same MRI technique that hospitals use to diagnose disease can <a href="https://www.acs.org/education/whatischemistry/landmarks/mri.html">also be used on chemical compounds</a> to work out their structure.</p>
<p>But even if a chemist guessed a completely new structure unrelated to any compound known on Earth, they’d still have to make it, which is the hard part. Figuring out that a chemical compound could exist does not tell you how it’s structured or what conditions you need to make it.</p>
<p>For many useful compounds, like <a href="https://www.nature.com/articles/ja2012126">penicillin</a>, it’s easier and cheaper to “grow” and extract them from moulds, plants or insects. Thus the scientists searching for new chemistry still often look for inspiration in the tiniest corners of the world around us.</p><img src="https://counter.theconversation.com/content/211302/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Addicoat receives funding from EPSRC and the Royal Society. </span></em></p>The limitless world of chemistry and how researchers investigate it.Matthew Addicoat, Senior Lecturer in Functional Materials, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1137612019-03-19T08:12:42Z2019-03-19T08:12:42ZWe did a breakthrough ‘speed test’ in quantum tunnelling, and here’s why that’s exciting<figure><img src="https://images.theconversation.com/files/264571/original/file-20190319-28468-3c5vq6.jpg?ixlib=rb-1.1.0&rect=44%2C0%2C5000%2C3125&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Future technologies will exploit today's advances in our understanding of the quantum world.</span> <span class="attribution"><span class="source">Shutterstock/PopTika </span></span></figcaption></figure><p>When you deal with things at the quantum scale, where things are very small, the world is quite fuzzy and bizarre in comparison to our everyday experiences.</p>
<p>For example, we can’t ordinarily walk through solid walls. But at the quantum scale, when a particle encounters a seemingly insurmountable barrier, it can sometimes pass through to the other side – a process known as quantum tunnelling.</p>
<p>But how fast a particle could tunnel through a barrier was always a puzzle.</p>
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<a href="https://theconversation.com/what-do-we-mean-by-meaning-science-can-help-with-that-113269">What do we mean by meaning? Science can help with that</a>
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<p>In work <a href="https://www.nature.com/articles/s41586-019-1028-3" title="Attosecond angular streaking and tunnelling time in atomic hydrogen">published today in Nature</a> we’ve solved part of the problem.</p>
<p>Why is that important? It’s a breakthrough that could have an impact on future technologies we see in our homes, at work or elsewhere.</p>
<p><a href="https://www.forbes.com/sites/chadorzel/2015/08/13/what-has-quantum-mechanics-ever-done-for-us/" title="What Has Quantum Mechanics Ever Done For Us?">Many of today’s technologies</a> – such as semiconductors, the LED screen on your smart phone, or lasers – are based on our understanding of how things work in the quantum world. </p>
<p>So the more we can learn, the more we can develop.</p>
<h2>Back to the tunnelling</h2>
<p>For quantum particles, such as electrons, when we say they can tunnel through barriers, we don’t refer to a physical obstacles, but barriers of energy. </p>
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<img alt="" src="https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Things behave differently in the quantum world.</span>
<span class="attribution"><span class="source">Shutterstock/VectorMine</span></span>
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<p>Tunnelling is possible due to the <a href="https://theconversation.com/explainer-what-is-wave-particle-duality-7414" title="Explainer: what is wave-particle duality">wave nature of the electron</a>. Quantum mechanics assigns wave nature to every particle, and hence there is always a finite probability for the wave to propagate through barriers, just as sound travels through walls. </p>
<p>It may sound counterintuitive, but this is what is exploited in technologies such as <a href="https://www.britannica.com/technology/scanning-tunneling-microscope">scanning tunnelling microscopes</a>, which allow scientists to create images with atomic resolution. This is also naturally observed in nuclear fusion, and in biological processes such as photosynthesis.</p>
<p>Although the phenomenon of quantum tunnelling is well studied and utilised, physicists still lacked a complete understanding of it, especially with regards to its dynamics. </p>
<p>If we could exploit the dynamics of tunnelling – for example, use it to carry more information – it could possibly give us a new handle on future quantum technologies. </p>
<h2>A tunnel speed test</h2>
<p>The first step towards this goal is to measure the speed of the tunnelling process. This is no simple feat, as the time scales involved in the measurement are extremely small. </p>
<p>For energy barriers the size of few billionths of a metre, as in our experiment, some physicists had calculated the tunnelling process would take around a hundred attoseconds (1 attosecond is a billionth of a billionth of a second). </p>
<p>To put things in perspective, if an attosecond is stretched to a second, then a second equals the age of the universe.</p>
<p>The estimated times are so extremely small that they were previously treated as practically instantaneous. Hence for our experiment we needed a clock that can time these events with enormous accuracy and precision. </p>
<p>The technological advancements in <a href="https://www.griffith.edu.au/centre-quantum-dynamics/our-research-groups/ultrafast-attosecond-science">ultrafast laser systems</a> enabled us to implement such a clock at the Australian Attosecond Science Facility, Centre for Quantum Dynamics, at Griffith University.</p>
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<span class="caption">Part of the experiment set up at the Griffith University lab.</span>
<span class="attribution"><span class="source">U. Satya Sainadh</span>, <span class="license">Author provided</span></span>
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<p>The clock in the experiment is not mechanical or electrical – rather it is the rotating electric field vector of an ultrafast laser pulse.</p>
<p>Light is just electromagnetic radiation made of electric and magnetic fields varying at a rapid rate. We used this rapidly changing field to induce tunnelling in atomic hydrogen and also as a stopwatch to measure when it ends. </p>
<h2>How fast?</h2>
<p>The choice of using atomic hydrogen (which is simply a bound pair of one electron and one proton) avoids the complications that arise from other atoms, making it easier to compare and interpret the results unambiguously. </p>
<p>The tunnelling time we measured was found to be no more than 1.8 attoseconds, much smaller than some theories had predicted. This measurement calls for a serious reconsideration of our understanding of tunnelling dynamics.</p>
<p>Various theories estimated a range of tunnelling times – from zero to hundreds of attoseconds – and there was no consensus among physicists on which single theoretical estimate was correct. </p>
<p>A basic reason for the disagreements lies in the very concept of time in quantum mechanics. Because of quantum uncertainties, there can be no absolute certainty in the time at which a particle enters into or emerges from the barrier.</p>
<p>But experiments like ours, using precise measurements on simple systems, could guide us in refining our understanding of such times </p>
<h2>The next technologies</h2>
<p>Quantum leaps in the technological world are often rooted in the quest for fundamental science.</p>
<p>Future quantum technologies that incorporates many of the quantum features – such as superposition and entanglement – will lead to what technologists call the “second quantum revolution”.</p>
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Read more:
<a href="https://theconversation.com/weve-designed-a-flux-capacitor-but-it-wont-take-us-back-to-the-future-92841">We've designed a 'flux capacitor', but it won't take us Back to the Future</a>
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<p>By fully understanding the quantum dynamics of the simplest possible atomic tunnelling event – with a single proton and a single electron – we have shown that certain types of theories can be relied on to give the right answer, where other types of theories fail. </p>
<p>This gives us confidence about what theories to apply to other, more complicated systems. </p>
<p>Measurements at the attosecond scale not only add an extra dimension for the future quantum technologies but also can fundamentally help in understanding the elephant of the quantum room: what is <em>time</em>? </p>
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<p><em><strong>You might also like</strong></em>: In <a href="https://theconversation.com/trust-me-im-an-expert-the-explainer-episode-96286">Trust Me, I’m An Expert: The explainer episode</a>, Andrew White, a professor in physics at the University of Queensland, tells us how far quantum mechanics has come, why the research hit a wall, and what exciting breakthroughs might be just around the corner.</p><img src="https://counter.theconversation.com/content/113761/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>U. Satya Sainadh receives funding from Technion for his research. </span></em></p>Things get weird at the quantum level and now we know they can happen really fast when a particle pushes through an almost insurmountable barrier.U. Satya Sainadh, Postdoctoral researcher, Technion - Israel Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1062202019-02-07T12:28:21Z2019-02-07T12:28:21ZLise Meitner – the forgotten woman of nuclear physics who deserved a Nobel Prize<figure><img src="https://images.theconversation.com/files/257317/original/file-20190205-86205-ff9763.jpg?ixlib=rb-1.1.0&rect=40%2C4%2C1556%2C1171&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lise Meitner was left off the publication that eventually led to a Nobel Prize for her colleague.</span> </figcaption></figure><p><a href="http://www.atomicarchive.com/Fission/Fission1.shtml">Nuclear fission</a> – the physical process by which very large atoms like uranium split into pairs of smaller atoms – is what makes <a href="https://www.atomicheritage.org/history/science-behind-atom-bomb">nuclear bombs</a> and <a href="http://www.world-nuclear.org/information-library/current-and-future-generation/outline-history-of-nuclear-energy.aspx">nuclear power plants</a> possible. But for many years, physicists believed it energetically impossible for atoms as large as uranium (atomic mass = 235 or 238) to be split into two.</p>
<p>That all changed on Feb. 11, 1939, with a <a href="https://www.nature.com/articles/143239a0">letter to the editor</a> of Nature – a premier international scientific journal – that described exactly how such a thing could occur and even named it fission. In that letter, physicist Lise Meitner, with the assistance of her young nephew <a href="http://www.atomicarchive.com/Bios/Frisch.shtml">Otto Frisch</a>, provided a physical explanation of how nuclear fission could happen.</p>
<p>It was a massive leap forward in nuclear physics, but today Lise Meitner remains obscure and largely forgotten. She was excluded from the victory celebration because she was a Jewish woman. Her story is a sad one.</p>
<h2>What happens when you split an atom</h2>
<p>Meitner based her fission argument on the “<a href="https://socratic.org/questions/how-does-the-liquid-drop-model-account-for-nuclear-fission">liquid droplet model</a>” of nuclear structure – a model that likened the forces that hold the atomic nucleus together to the surface tension that gives a water droplet its structure.</p>
<p>She noted that the surface tension of an atomic nucleus weakens as the charge of the nucleus increases, and could even approach zero tension if the nuclear charge was very high, as is the case for uranium (charge = 92+). The lack of sufficient nuclear surface tension would then allow the nucleus to split into two fragments when struck by a <a href="https://sciencenotes.org/neutron-definition-chemistry/">neutron</a> – a chargeless subatomic particle – with each fragment carrying away very high levels of kinetic energy. Meisner remarked: “The whole ‘fission’ process can thus be described in an essentially classical [physics] way.” Just that simple, right?</p>
<p>Meitner went further to explain how her scientific colleagues had gotten it wrong. When scientists bombarded uranium with neutrons, they believed the uranium nucleus, rather than splitting, captured some neutrons. These captured neutrons were then converted into positively charged protons and thus transformed the uranium into the incrementally larger elements on the <a href="https://www.livescience.com/25300-periodic-table.html">periodic table of elements</a> – the so-called “<a href="https://www.britannica.com/science/transuranium-element">transuranium</a>,” or beyond uranium, elements.</p>
<p>Some people were skeptical that neutron bombardment could produce transuranium elements, including <a href="https://www.atomicheritage.org/profile/irene-joliot-curie">Irene Joliot-Curie</a> – Marie Curie’s daughter – and Meitner. Joliot-Curie had found that one of these new alleged transuranium elements actually behaved chemically just like <a href="https://www.livescience.com/39623-facts-about-radium.html">radium</a>, the element her mother had discovered. Joliot-Curie suggested that it might be just radium (atomic mass = 226) – an element somewhat smaller than uranium – that was coming from the neutron-bombarded uranium.</p>
<p>Meitner had an alternative explanation. She thought that, rather than radium, the element in question might actually be <a href="https://www.livescience.com/37581-barium.html">barium</a> – an element with a chemistry very similar to radium. The issue of radium versus barium was very important to Meitner because barium (atomic mass = 139) was a possible fission product according to her split uranium theory, but radium was not – it was too big (atomic mass = 226).</p>
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<figcaption>
<span class="caption">When a neutron bombards a uranium atom, the uranium nucleus splits into two different smaller nuclei.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Kernspaltung.svg">Stefan-Xp/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Meitner urged her chemist colleague <a href="https://www.atomicheritage.org/profile/otto-hahn">Otto Hahn</a> to try to further purify the uranium bombardment samples and assess whether they were, in fact, made up of radium or its chemical cousin barium. Hahn complied, and he found that Meitner was correct: the element in the sample was indeed barium, not radium. Hahn’s finding suggested that the uranium nucleus had split into pieces – becoming two different elements with smaller nuclei – just as Meitner had suspected.</p>
<h2>As a Jewish woman, Meitner was left behind</h2>
<p>Meitner should have been the hero of the day, and the physicists and chemists should have jointly published their findings and waited to receive the world’s accolades for their discovery of nuclear fission. But unfortunately, that’s not what happened.</p>
<p>Meitner had two difficulties: She was a Jew living as an exile in Sweden because of the Jewish persecution going on in Nazi Germany, and she was a woman. She might have overcome either one of these obstacles to scientific success, but both proved insurmountable.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=793&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=793&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=793&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=996&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=996&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=996&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lise Meitner and Otto Hahn in Berlin, 1913.</span>
</figcaption>
</figure>
<p>Meitner had been working as Hahn’s academic equal when they were on the faculty of the Kaiser Wilhelm Institute in Berlin together. By all accounts they were close colleagues and friends for many years. When the Nazis took over, however, Meitner was forced to leave Germany. She took a position in Stockholm, and continued to work on nuclear issues with Hahn and his junior colleague Fritz Strassmann through regular correspondence. This working relationship, though not ideal, was still highly productive. The barium discovery was the latest fruit of that collaboration. </p>
<p>Yet when it came time to publish, Hahn knew that including a Jewish woman on the paper would cost him his career in Germany. So he <a href="https://doi.org/10.1007/BF01488241">published without her</a>, falsely claiming that the discovery was based solely on insights gleaned from his own chemical purification work, and that any physical insight contributed by Meitner played an insignificant role. All this despite the fact he wouldn’t have even thought to isolate barium from his samples had Meitner not directed him to do so.</p>
<p>Hahn had trouble explaining his own findings, though. In his paper, he put forth no plausible mechanism as to how uranium atoms had split into barium atoms. But Meitner had the explanation. So a few weeks later, Meitner wrote her famous fission letter to the editor, ironically explaining the mechanism of “Hahn’s discovery.”</p>
<p>Even that didn’t help her situation. The Nobel Committee awarded the <a href="https://www.nobelprize.org/prizes/chemistry/1944/summary/">1944 Nobel Prize in Chemistry</a> “for the discovery of the fission of heavy nuclei” to Hahn alone. Paradoxically, the word “fission” never appeared in Hahn’s original publication, as Meitner had been the first to coin the term in the letter published afterward. </p>
<p>A controversy has raged about the discovery of nuclear fission ever since, with <a href="https://www.ucpress.edu/book/9780520208605/lise-meitner">critics claiming</a> it represents one of the worst examples of blatant racism and sexism by the Nobel committee. Unlike another prominent female nuclear physicist whose career preceded her – <a href="https://www.nobelprize.org/prizes/chemistry/1911/marie-curie/facts/">Marie Curie</a> – Meitner’s contributions to nuclear physics were never recognized by the Nobel committee. She has been totally left out in the cold, and remains unknown to most of the public.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=561&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=561&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=561&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Meitner received the Enrico Fermi Award in 1966. Her nephew Otto Frisch is on the left.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/iaea_imagebank/4311592724">IAEA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>After the war, Meitner remained in Stockholm and became a Swedish citizen. Later in life, she decided to let bygones be bygones. She reconnected with Hahn, and the two octogenarians resumed their friendship. Although the Nobel committee never acknowledged its mistake, the slight to Meitner was partly mitigated in 1966 when the U.S. Department of Energy jointly awarded her, Hahn and Strassmann its prestigious <a href="https://science.energy.gov/fermi/">Enrico Fermi Award</a> “for pioneering research in the naturally occurring radioactivities and extensive experimental studies leading to the discovery of fission.” The two-decade late recognition came just in time for Meitner. She and Hahn died within months of each other in 1968; they were both 89 years old.</p><img src="https://counter.theconversation.com/content/106220/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy J. Jorgensen does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Left off publications due to Nazi prejudice, this Jewish woman lost her rightful place in the scientific pantheon as the discoverer of nuclear fission.Timothy J. Jorgensen, Director of the Health Physics and Radiation Protection Graduate Program and Associate Professor of Radiation Medicine, Georgetown UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1055642018-12-20T11:34:09Z2018-12-20T11:34:09ZDavid vs. Goliath: What a tiny electron can tell us about the structure of the universe<figure><img src="https://images.theconversation.com/files/247814/original/file-20181128-32230-mojlgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of electrons orbiting the nucleus.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/success?u=http%3A%2F%2Fdownload.shutterstock.com%2Fgatekeeper%2FW3siZSI6MTU0MzQ1OTQ5MCwiYyI6Il9waG90b19zZXNzaW9uX2lkIiwiZGMiOiJpZGxfMTM0NTU2MjQ4IiwiayI6InBob3RvLzEzNDU1NjI0OC9odWdlLmpwZyIsIm0iOjEsImQiOiJzaHV0dGVyc3RvY2stbWVkaWEifSwia3hoTU15VWRSM21XSEF0UEh2SEZjUGJkdHNFIl0%2Fshutterstock_134556248.jpg&pi=33421636&m=134556248&src=ZLYMmD6NnpDeuys3xFAYMQ-1-32">Roman Sigaev/ Shutterstock.com</a></span></figcaption></figure><p>What is the shape of an electron? If you recall pictures from your high school science books, the answer seems quite clear: an electron is a small ball of negative charge that is smaller than an atom. This, however, is quite far from the truth.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=500&fit=crop&dpr=1 600w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=500&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=500&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=628&fit=crop&dpr=1 754w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=628&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=628&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A simple model of an atom with the nucleus of made of protons, which have a positive charge, and neutrons, which are neutral. The electrons, which have a negative charge, orbit the nucleus.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/atom-scientific-poster-atomic-structure-nucleus-1067668175?src=q1VjPFk6YNxYoapF9IhEbA-1-36">Vector FX / Shutterstock.com</a></span>
</figcaption>
</figure>
<p>The <a href="https://en.wikipedia.org/wiki/Electron">electron</a> is commonly known as one of the main components of atoms making up the world around us. It is the electrons surrounding the nucleus of every atom that determine how chemical reactions proceed. Their uses in industry are abundant: from electronics and welding to imaging and advanced particle accelerators. Recently, however, a physics experiment called <a href="https://www.nature.com/articles/s41586-018-0599-8">Advanced Cold Molecule Electron EDM</a> (ACME) put an electron on the center stage of scientific inquiry. The question that the ACME collaboration tried to address was deceptively simple: What is the shape of an electron? </p>
<h2>Classical and quantum shapes?</h2>
<p>As far as physicists currently know, electrons have no internal structure – and thus no shape in the classical meaning of this word. In the modern language of particle physics, which tackles the behavior of objects smaller than an atomic nucleus, the fundamental blocks of matter are continuous fluid-like substances known as “quantum fields” that permeate the whole space around us. In this language, an electron is perceived as a quantum, or a particle, of the “electron field.” Knowing this, does it even make sense to talk about an electron’s shape if we cannot see it directly in a microscope – or any other optical device for that matter?</p>
<p>To answer this question we must adapt our definition of shape so it can be used at incredibly small distances, or in other words, in the realm of quantum physics. Seeing different shapes in our macroscopic world really means detecting, with our eyes, the rays of light bouncing off different objects around us. </p>
<p>Simply put, we define shapes by seeing how objects react when we shine light onto them. While this might be a weird way to think about the shapes, it becomes very useful in the subatomic world of quantum particles. It gives us a way to define an electron’s properties such that they mimic how we describe shapes in the classical world. </p>
<p>What replaces the concept of shape in the micro world? Since light is nothing but a combination of oscillating <a href="https://en.wikipedia.org/wiki/Electric_field">electric</a> and <a href="https://en.wikipedia.org/wiki/Magnetic_field">magnetic</a> fields, it would be useful to define quantum properties of an electron that carry information about how it responds to applied electric and magnetic fields. Let’s do that.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This is the apparatus the physicists used to perform the ACME experiment.</span>
<span class="attribution"><a class="source" href="http://sitn.hms.harvard.edu/flash/2014/looking-closer-the-search-for-the-electron-electric-dipole-moment/">Harvard Department of Physics</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Electrons in electric and magnetic fields</h2>
<p>As an example, consider the simplest property of an electron: its electric charge. It describes the force – and ultimately, the acceleration the electron would experience – if placed in some external electric field. A similar reaction would be expected from a negatively charged marble – hence the “charged ball” analogy of an electron that is in elementary physics books. This property of an electron – its charge – survives in the quantum world. </p>
<p>Likewise, another “surviving” property of an electron is called the magnetic dipole moment. It tells us how an electron would react to a magnetic field. In this respect, an electron behaves just like a tiny bar magnet, trying to orient itself along the direction of the magnetic field. While it is important to remember not to take those analogies too far, they do help us see why physicists are interested in measuring those quantum properties as accurately as possible. </p>
<p>What quantum property describes the electron’s shape? There are, in fact, several of them. The simplest – and the most useful for physicists – is the one called the electric dipole moment, or EDM. </p>
<p>In classical physics, EDM arises when there is a spatial separation of charges. An electrically charged sphere, which has no separation of charges, has an EDM of zero. But imagine a dumbbell whose weights are oppositely charged, with one side positive and the other negative. In the macroscopic world, this dumbbell would have a non-zero electric dipole moment. If the shape of an object reflects the distribution of its electric charge, it would also imply that the object’s shape would have to be different from spherical. Thus, naively, the EDM would quantify the “dumbbellness” of a macroscopic object. </p>
<h2>Electric dipole moment in the quantum world</h2>
<p>The story of EDM, however, is very different in the quantum world. There the vacuum around an electron is not empty and still. Rather it is populated by various subatomic particles zapping into virtual existence for short periods of time. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=421&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=421&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=421&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=529&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=529&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=529&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Standard Model of particle physics has correctly predicted all of these particles. If the ACME experiment discovered that the electron had an EDM, it would suggest there were other particles that had not yet been discovered.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/diagram-standard-model-particle-physics-178784918?src=xfhHfcHQIOt6RTTLrx9c2Q-1-4">Designua/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>These virtual particles form a “cloud” around an electron. If we shine light onto the electron, some of the light could bounce off the virtual particles in the cloud instead of the electron itself. </p>
<p>This would change the numerical values of the electron’s charge and magnetic and electric dipole moments. Performing very accurate measurements of those quantum properties would tell us how these elusive virtual particles behave when they interact with the electron and if they alter the electron’s EDM.</p>
<p>Most intriguing, among those virtual particles there could be new, unknown species of particles that we have not yet encountered. To see their effect on the electron’s electric dipole moment, we need to compare the result of the measurement to theoretical predictions of the size of the EDM calculated in the currently accepted theory of the Universe, the <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">Standard Model</a>. </p>
<p>So far, the Standard Model accurately described all laboratory measurements that have ever been performed. Yet, it is unable to address many of the most fundamental questions, such as <a href="https://www.scientificamerican.com/article/what-is-antimatter-2002-01-24/">why matter dominates over antimatter throughout the universe</a>. The Standard Model makes a prediction for the electron’s EDM too: it requires it to be so small that ACME would have had no chance of measuring it. But what would have happened if ACME actually detected a non-zero value for the electric dipole moment of the electron? </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">View of the Large Hadron Collider in its tunnel near Geneva, Switzerland. In the LHC two counter-rotating beams of protons are accelerated and forced to collide, generating various particles.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/SWITZERLAND-CERN-LHC-CRYOGENIC-SYSTEM/b3aef1c7c68a4092a95939b1ca9d36ec/13/0">AP Photo/KEYSTONE/Martial Trezzini</a></span>
</figcaption>
</figure>
<h2>Patching the holes in the Standard Model</h2>
<p>Theoretical models have been proposed that fix shortcomings of the Standard Model, predicting the existence of <a href="https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model">new heavy particles</a>. These models may fill in the gaps in our understanding of the universe. To verify such models we need to prove the existence of those new heavy particles. This could be done through large experiments, such as those at the international <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider (LHC)</a> by directly producing new particles in high-energy collisions.</p>
<p>Alternatively, we could see how those new particles alter the charge distribution in the “cloud” and their effect on electron’s EDM. Thus, unambiguous observation of electron’s dipole moment in ACME experiment would prove that new particles are in fact present. That was the goal of the ACME experiment.</p>
<p>This is the reason why a <a href="https://www.nature.com/articles/s41586-018-0599-8">recent article in Nature</a> about the electron caught my attention. Theorists like <a href="https://scholar.google.com/citations?user=61U_XlgAAAAJ&hl=en&oi=ao">myself</a> use the results of the measurements of electron’s EDM – along with other measurements of properties of other elementary particles – to help to identify the new particles and make predictions of how they can be better studied. This is done to clarify the role of such particles in our current understanding of the universe. </p>
<p>What should be done to measure the electric dipole moment? We need to find a source of very strong electric field to test an electron’s reaction. One possible source of such fields can be found inside molecules such as thorium monoxide. This is the molecule that ACME used in their experiment. Shining carefully tuned lasers at these molecules, a reading of an electron’s electric dipole moment could be obtained, provided it is not too small. </p>
<p>However, as it turned out, it is. Physicists of the ACME collaboration did not observe the electric dipole moment of an electron – which suggests that its value is too small for their experimental apparatus to detect. This fact has important implications for our understanding of what we could expect from the Large Hadron Collider experiments in the future.</p>
<p>Interestingly, the fact that the ACME collaboration did not observe an EDM actually rules out the existence of heavy new particles that could have been easiest to detect at the LHC. This is a remarkable result for a tabletop-sized experiment that affects both how we would plan direct searches for new particles at the giant Large Hadron Collider, and how we construct theories that describe nature. It is quite amazing that studying something as small as an electron could tell us a lot about the universe.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UIflReRmynk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A short animation describing the physics behind EDM and ACME collaboration’s findings.</span></figcaption>
</figure><img src="https://counter.theconversation.com/content/105564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexey Petrov receives funding from US Department of Energy. </span></em></p>What shape is an electron? The answer, believe it or not, has implications for our understanding of the entire universe, and could reveal whether there are mysterious particles still to be discovered.Alexey A Petrov, Professor of Physics, Wayne State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/528222017-04-02T19:32:41Z2017-04-02T19:32:41ZThe periodic table: from its classic design to use in popular culture<figure><img src="https://images.theconversation.com/files/113029/original/image-20160226-26723-15gnsbs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The periodic table of the elements on a T-shirt.</span> <span class="attribution"><a class="source" href="http://mirror-au-nsw1.gallery.hd.org/_c/textures/_more2005/_more05/periodic-table-of-the-elements-printed-on-ancient-cotton-T-shirt-rotated-lowres-DHD.jpg.html">Damon Hart Davis</a></span></figcaption></figure><p>The periodic table is one of those classic images that you find in many science labs and classrooms. It’s an image almost everyone has seen at some time in their life.</p>
<p>You can also find the periodic table on <a href="https://www.questacon.edu.au/qshop/Questacon-Periodic-Table-T-shirt/">t-shirts</a>, <a href="http://shop.australiangeographic.com.au/mug-periodic-table.html">mugs</a>, <a href="https://www.getdigital.eu/Periodic-Table-Beach-Towel.html">beach towels</a>, <a href="https://www.amazon.com/Periodic-Chemical-Elements-Novelty-Pillowcase/dp/B00QFJXNVS">pillowcases</a> and <a href="http://www.cafepress.com.au/+periodic-table-chemical-elements+duvet-covers">duvet covers</a>, and <a href="http://www.cafepress.com.au/+periodic-table+gifts">plenty of other items</a>. It even inspired a <a href="https://www.theguardian.com/science/2009/oct/09/primo-levi-periodic-table">collection of short stories</a>. </p>
<p>Who can forget the periodic table put to music by the American <a href="http://www.allmusic.com/artist/tom-lehrer-mn0000611877/biography">Tom Lehrer</a>, a Harvard mathematics professor who was also a singer/songwriter and satirist. His song, The Elements, includes all the elements that were known at the time of writing in 1959.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zGM-wSKFBpo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Since then, several new elements have been added to the periodic table, including the <a href="https://theconversation.com/four-new-elements-named-heres-how-the-periodic-table-evolved-60276">four</a> that were <a href="https://iupac.org/iupac-announces-the-names-of-the-elements-113-115-117-and-118/">formally approved last year</a> by the International Union of Pure and Applied Chemistry (IUPAC).</p>
<p>But what exactly does the periodic table show?</p>
<p>In brief, it is an attempt to organise the collection of the elements – all of the known pure compounds made from a single type of atom.</p>
<p>There are two ways to look at how the periodic table is constructed, based on either the observed properties of the elements contained within it, or on the subatomic construction of the atoms that form each element.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=484&fit=crop&dpr=1 754w, https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=484&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/155128/original/image-20170201-12656-1hd5emj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=484&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The basic modern periodic table.</span>
<span class="attribution"><span class="source">Shutterstock/duntaro</span></span>
</figcaption>
</figure>
<h2>The elements</h2>
<p>When scientists began collecting elements in the 1700s and 1800s, slowly identifying new ones over decades of research, they began to notice patterns and similarities in their physical properties. Some were gases, some were shiny metals, some reacted violently with water, and so on. </p>
<p>At the time when elements were first being discovered, the structure of atoms was not known. Scientists began to look at ways to arrange them systematically so that similar properties could be grouped together, just as someone collecting seashells might try to organise them by shape or colour.</p>
<p>The task was made more difficult because not all of the elements were known. This left gaps, which made deciphering patterns a bit like trying to assemble a jigsaw puzzle with missing pieces.</p>
<p>Different scientists came up with different types of tables. The first version of the current table is generally attributed to Russian chemistry professor <a href="http://www.britannica.com/biography/Dmitry-Ivanovich-Mendeleyev">Dmitri Mendeleev</a> in 1869, with an updated version in 1871.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116741/original/image-20160330-28455-1ror2vj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mendeleev’s periodic table is first published outside Russia in Zeitschrift für Chemie (1869, pages 405-6).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Mendeleev%27s_periodic_table_(1869).svg">Wikimedia/Dimitri Mendeleev</a></span>
</figcaption>
</figure>
<p>Importantly, Mendeleev left gaps in the table where he thought missing elements should be placed. Over time, these gaps were filled in and the final version as we know it today emerged.</p>
<h2>The atoms</h2>
<p>To really understand the final structure of the periodic table, we need to understand a bit about atoms and how they are constructed. Atoms have a central core (the nucleus) made up of smaller particles called protons and neutrons.</p>
<p>It is the number of protons that gives an element its atomic number – the number generally found in the top left corner of each box in the periodic table. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=195&fit=crop&dpr=1 600w, https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=195&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=195&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=245&fit=crop&dpr=1 754w, https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=245&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/155129/original/image-20170201-12685-525wu2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=245&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The properties of hydrogen as marked on the periodic table.</span>
<span class="attribution"><span class="source">Shutterstock/duntaro</span></span>
</figcaption>
</figure>
<p>The periodic table is arranged in order of increasing atomic number (left to right, top to bottom). It ranges from element 1 (hydrogen <a href="http://www.rsc.org/periodic-table/element/1/hydrogen">H</a>) in the top left, to the newly approved element 118 (oganesson <a href="http://www.rsc.org/periodic-table/element/118/oganesson">Og</a>) in the bottom right.</p>
<p>The number of neutrons in the nucleus can vary. This gives rise to different isotopes for every element. </p>
<p>For example, you may have heard of <a href="http://science.howstuffworks.com/environmental/earth/geology/carbon-14.htm">carbon-14 dating</a> to determine the age of objects. This isotope is a radioactive version of normal carbon <a href="http://www.rsc.org/periodic-table/element/6/carbon">C</a> (or carbon-12) that has two extra neutrons.</p>
<p>But why is there a separate box of elements below the main table, and why is the main table an odd shape, with a bite taken out of the top? That comes down to how the other component of the atom – the electrons – are arranged.</p>
<h2>The electrons</h2>
<p>We tend to think of atoms as built a bit like onions, with seven layers of electrons called “shells”, labelled K, L, M, N, O, P, and Q, surrounding the core nucleus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=318&fit=crop&dpr=1 600w, https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=318&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=318&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/126483/original/image-20160614-29205-4s6tgg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Think of the atom with a central nucleus that contains all the protons and neutrons, surrounded by a series of shells that contain the electrons.</span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Each row in the periodic table sort of corresponds to filling up one of these shells with electrons. Each shell has subshells, and the order in which the shells/subshells get filled is based on the energy required, although it’s a complicated process. We’ll come back to these later.</p>
<p>In simple terms, the first element in each row starts a new shell containing one electron, while the last element in each row has two (or one for the the first row) of the subshells in the outer shell fully occupied. These differences in electrons also account for some of the similarities in properties between elements. </p>
<p>With the one or two subshells in the outer layer full of electrons, the last elements of each row are quite unreactive, as there are no holes or gaps in the outer shell to interact with other atoms.</p>
<p>This is why elements in the last column, such as helium <a href="http://www.rsc.org/periodic-table/element/2/helium">He</a>, neon (<a href="http://www.rsc.org/periodic-table/element/10/neon">Ne</a>), argon (<a href="http://www.rsc.org/periodic-table/element/18/argon">Ar</a>) and so on, are called the <a href="http://www.britannica.com/science/noble-gas">noble gases</a> (or inert gases). They are all gases and they are “noble” because they rarely associate with other elements.</p>
<p>In contrast, the elements of the first column, with the exception of hydrogen (just like English grammar, there’s always an exception!), are called alkali metals. The first-column elements are metal-like in character, but with only one electron in the outer shell, they are very reactive as this lone electron is very easy to engage in chemical bonding. When added to water, they quickly react to form an alkaline (basic) solution.</p>
<p>Each shell can accommodate an increasing number of electrons. The first shell (K) only fits two, so the first row of the periodic table has only two elements: hydrogen (<a href="http://www.rsc.org/periodic-table/element/1/hydrogen">H</a>) with one electron, and helium (<a href="http://www.rsc.org/periodic-table/element/2/helium">He</a>) with two.</p>
<p>The second shell (L) fits eight electrons. Thus the second row of the periodic table contains eight elements, with a gap left between hydrogen and helium to accommodate the extra six. </p>
<p>The third shell (M) fits 18 electrons, but the third row still only has eight elements. This is because the extra ten electrons don’t get added to this layer until after the first two electrons are added to the fourth shell (N) (we’ll get to why, later).</p>
<p>So the gap is expanded in the fourth row to accommodate the additional ten elements, leading to the “bite” out of the top of the table. The extra ten compounds in the middle section are called the <a href="http://www.britannica.com/science/transition-element">transition metals</a>.</p>
<p>The fourth shell holds 32 electrons, but again the extra electrons are not added to this shell until some have also been added to the fifth (O) and sixth (P) shells, meaning that both the fourth and fifth rows hold 18 elements. </p>
<p>For the next two rows (sixth and seventh), rather than further expanding the table sideways to include these extra 14 elements, which would make it too wide to easily read, they have been inserted as a block of two rows, called the <a href="http://www.britannica.com/science/lanthanoid">lanthanoids</a> (elements 57 to 71) and <a href="http://www.britannica.com/science/actinoid-element">actinoids</a> (elements 89 to 103), below the main table.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=359&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=359&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=359&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=451&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=451&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154931/original/image-20170131-13243-135rr77.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=451&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The periodic table would look very different if the lanthanoids and actinoids were inserted within the table.</span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>You can see where they would fit in if the periodic table was widened, if you look at the bottom two squares in the third column of the table above.</p>
<h2>Across the columns</h2>
<p>There is another complicating factor leading to the final shape of the table. As mentioned earlier, as the electrons are added to each layer they go into different subshells (or orbitals), which describes locations around the nucleus where they are most likely to be found. These are known by the letters s, p, d and f.</p>
<p>The letters used for the orbitals are actually derived from descriptions of the emission or absorption of light due to electrons moving between the orbitals: <strong>s</strong>harp, <strong>p</strong>rincipal, <strong>d</strong>iffuse and <strong>f</strong>undamental.</p>
<p>Each shell has its own configuration of subshells named from 1s through to 7p, which gives the total number of electrons in each shell as we progress through the periodic table. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=489&fit=crop&dpr=1 600w, https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=489&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=489&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=615&fit=crop&dpr=1 754w, https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=615&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/163552/original/image-20170402-27256-u5wjt7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=615&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As mentioned earlier the order in which the subshells fill with electrons is not so straightforward. You can see the order in which they fill from the image below, just follow the order as you would read down from left to right.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=444&fit=crop&dpr=1 754w, https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=444&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/163745/original/image-20170403-21969-flm80p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=444&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>There is an <a href="http://www.ptable.com/#Orbital">interactive periodic table</a> that also illustrates the filling sequence well if you click through the atoms.</p>
<p>Elements within a column generally have similar properties, but in some places elements side by side can also be similar. For example, in the transition metals the cluster of precious metals around copper (<a href="http://www.rsc.org/periodic-table/element/29/copper">Cu</a>), silver (<a href="http://www.rsc.org/periodic-table/element/47/silver">Ag</a>), gold (<a href="http://www.rsc.org/periodic-table/element/79/gold">Au</a>), palladium (<a href="http://www.rsc.org/periodic-table/element/46/palladium">Pd</a>) and platinum (<a href="http://www.rsc.org/periodic-table/element/78/platinum">Pt</a>) are quite alike.</p>
<p>Most of the existing elements with high atomic numbers, including the <a href="https://theconversation.com/the-race-to-find-even-more-new-elements-to-add-to-the-periodic-table-52747">four superheavy elements added last year</a>, are very unstable and have never been detected in, or isolated from, nature. </p>
<p>Instead, they are created and analysed in minute quantities under highly artificial conditions. Theoretically, there could be further elements beyond the 118 now known (there are additional g, h and i suborbitals), but we don’t know yet if any of these would be stable enough to be isolated.</p>
<h2>A classic design</h2>
<p>The periodic table has seen many colourful and informative versions created over the years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/150468/original/image-20161216-26116-qgzp6m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Periodic table decorates a taxi in the UK.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/gashwin/6959094671/">Flickr/Fr Gaurav Shroff</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>One of my favourites is an <a href="http://www.raci.org.au/periodic-table-on-show">artistic version</a> with original artworks for each element commissioned by the Royal Australian Chemical Institute to celebrate the International Year of Chemistry in 2011.</p>
<p>Another favourite is an <a href="http://www.periodictable.com/index.html">interactive version</a> with pictures of the elements. The creators of this site have also published a coffee table book called <a href="http://www.periodictable.com/Posters/index.theelements.html">The Elements</a> and an <a href="http://www.periodictable.com/Posters/index.theelementsipad.html">Apple app</a> with videos of each element.</p>
<p><a href="http://www.rsc.org/periodic-table">Interactive versions</a> have also been created by the Royal Society of Chemistry (and can also be downloaded as an app) and <a href="http://www.chemeddl.org/resources/ptl/index.php">ChemEd DL</a> among others.</p>
<p>The classic design of the periodic table can be used to play a version of the <a href="http://teachbesideme.com/periodic-table-battleship/">Battleship</a> game.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118104/original/image-20160411-6250-1lbc5v4.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Playing battleships with the periodic table at the first World Science Festival Brisbane in 2016.</span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>There are also many fun versions created to help organise a multitude of objects, including <a href="http://grafikdzine.deviantart.com/art/Periodic-Food-Table-114678046">food</a>, <a href="http://beergeno.me/wp-content/uploads/2010/10/Per_iodic_Table_Beer_Styles.png">beer</a>, <a href="http://www.fastcocreate.com/3039715/ge-drops-some-social-science-with-the-periodic-table-of-emojis">emojis</a>, <a href="http://ictevangelist.com/wp-content/uploads/2014/07/PTAPPS-ICTEvangelist.png">iPad apps</a> and <a href="http://grosdino.deviantart.com/art/Periodic-Table-of-the-Birds-401058406">birds</a>.</p>
<p>As for Tom Lehrer’s The Elements, the song has yet to be updated to include all the elements known today but it has been covered by other people over the years. </p>
<p>Actor Daniel Radcliffe, of Harry Potter fame, performed a version during a guest appearance on the BBC’s Graham Norton Show.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rSAaiYKF0cs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>There are <a href="https://www.youtube.com/watch?v=VgVQKCcfwnU">other musical versions</a> of the elements but they too have yet to be updated to include all entries of the periodic table.</p>
<p>In summary, the periodic table is the chemist’s taxonomy of all elements. Its triumph is that it is still highly relevant to scientists, while also becoming embedded in popular culture.</p><img src="https://counter.theconversation.com/content/52822/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Blaskovich receives funding from the Australian National Health and Medical Research Council (NHMRC) and the Wellcome Trust. He is a member of the Royal Australian Chemical Institute and the American Chemical Society.</span></em></p>The periodic table is one of the classic images of science that is found in labs as well as on t-shirts, mugs, even set to music. But what exactly is the periodic table?Mark Blaskovich, Senior Research Officer, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/528622016-01-07T05:46:10Z2016-01-07T05:46:10ZThe search for new elements on the periodic table started with a blast<figure><img src="https://images.theconversation.com/files/107484/original/image-20160107-14970-1tvxwlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New elements were discovered in early thermonuclear bomb tests.</span> <span class="attribution"><a class="source" href="https://pixabay.com/en/nuclear-weapons-test-nuclear-weapon-67557/">Pixabay</a></span></figcaption></figure><p>So the periodic table has expanded again with the addition late last year of <a href="https://theconversation.com/the-race-to-find-even-more-new-elements-to-add-to-the-periodic-table-52747">four new superheavy elements</a>, bringing the known total up to 118.</p>
<p>But the hunt for new elements started with efforts to develop nuclear power and the atomic bomb during World War II. At the time, <a href="http://www.rsc.org/periodic-table/element/92/uranium">uranium</a> was the heaviest known element, sitting at number 92 in the periodic table. </p>
<p>Researchers quickly discovered that when uranium is placed in a nuclear reactor, a complex sequence of interactions leads to the production of several so-called <a href="http://www.britannica.com/science/transuranium-element">transuranic elements</a> (elements beyond uranium).</p>
<p>Probing around in the debris of the first hydrogen bomb test revealed two further transuranic elements, <a href="http://www.rsc.org/periodic-table/element/99/einsteinium">einsteinium</a> and <a href="http://www.rsc.org/periodic-table/element/100/fermium">fermium</a>, bringing the total to an even 100. </p>
<p>Some of these elements are more commonly encountered that you might think. Most families would own some <a href="http://www.rsc.org/periodic-table/element/95/americium">americium</a> (element number 95) in the form of an every-day smoke detector, and <a href="http://www.rsc.org/periodic-table/element/98/californium">californium</a> (number 98) is widely used in industrial analysers. At a cool <a href="http://web.ornl.gov/%7Ewebworks/cpr/pres/107270_.pdf">US$60 million dollars per gram</a>, however, californium is about a million times more expensive than gold.</p>
<h2>Beyond the century element</h2>
<p>Beyond element 100, not even a hydrogen bomb is powerful enough to make progress, and scientists had to change tack in their quest for ever heavier elements. They substituted finesse for brute force, using particle accelerators to fire atoms onto carefully chosen targets. </p>
<p>Under the right conditions, the nuclei of atoms in the beam and target can fuse together and produce new elements. Fittingly, the first element made in this way, <a href="http://www.rsc.org/periodic-table/element/101/mendelevium">mendelevium</a>, was named after Dimitri Mendeleev, the creator of the periodic table.</p>
<p>Russian and American scientists continued to push forward through the 1950s, 60s and 70s, eventually reaching element <a href="http://www.rsc.org/periodic-table/element/106/seaborgium">106</a>. Reflecting the tensions of the Cold War years, priority for discovering these elements was strongly contested, with claims and counterclaims over ambiguous experimental results.</p>
<p>Not until 1997 did the International Union of Pure and Applied Chemistry (<a href="http://www.iupac.org/">IUPAC</a>) credit the discoverers of these elements and announce official names, mostly based on US and Soviet scientists and cities.</p>
<p>The Germans picked up the baton in the 1980s and 90s, discovering elements <a href="http://www.rsc.org/periodic-table/element/107/bohrium">107</a> through to <a href="http://www.rsc.org/periodic-table/element/112/copernicium">112</a>.</p>
<p>German researchers added a strongly European flavour to the naming scheme, honouring the physicists Niels Bohr (<a href="http://www.rsc.org/periodic-table/element/107/bohrium">bohrium</a>), Lise Meitner (<a href="http://www.rsc.org/periodic-table/element/109/meitnerium">meitnerium</a>), and Wilhelm Röntgen (<a href="http://www.rsc.org/periodic-table/element/111/roentgenium">roentgenium</a>), the astronomer Nicolaus Copernicus (<a href="http://www.rsc.org/periodic-table/element/112/copernicium">copernicium</a>) and their home city and state – <a href="http://www.rsc.org/periodic-table/element/110/darmstadtium">darmstadtium</a> and <a href="http://www.rsc.org/periodic-table/element/108/hassium">Hassium</a> are named after the town of Darmstadt and the German state of Hesse (passing through Latin along the way, which changes the ‘e’ to an ‘a’. Nothing’s ever simple!).</p>
<p>Only a handful of atoms of these elements have ever been produced.</p>
<h2>Let’s get super-heavy</h2>
<p>Moving on to still heavier elements, the hunt becomes increasingly difficult for three reasons.</p>
<p>First, the probability of two nuclei successfully fusing to form a new element rapidly decreases. Second, these super-heavy elements are extremely unstable, so any atoms produced have a fleeting existence. And third, it becomes increasingly difficult to untangle the complex signatures that reveal their momentary creation and decay.</p>
<p>Reflecting improved international relations in the post-Glasnost era, most of the recent discoveries have been credited to collaborations between US and Russian researchers. Elements 114 (<a href="http://www.rsc.org/periodic-table/element/114/flerovium">flerovium</a>) and 116 (<a href="http://www.rsc.org/periodic-table/element/116/livermorium">livermorium</a>) were announced by the IUPAC in 2012.</p>
<p>The <a href="http://www.iupac.org/news/news-detail/article/discovery-and-assignment-of-elements-with-atomic-numbers-113-115-117-and-118.html">most recent announcement</a> awards discovery of elements <a href="http://www.rsc.org/periodic-table/element/115/">115</a>, <a href="http://www.rsc.org/periodic-table/element/117/">117</a> and <a href="http://www.rsc.org/periodic-table/element/118/">118</a> to the same groups. A Japanese team, working independently, has been recognised for element <a href="http://www.rsc.org/periodic-table/element/113/">113</a>.</p>
<p>Producing even a sniff of these super-heavy elements is a heroic endeavour. To discover element 118, for example, experimenters fired a beam of calcium atoms for months at a time onto a target loaded with the element californium.</p>
<p>The odds of any one calcium atom fusing is tiny, roughly the same as winning the Oz Lotto jackpot, but then being killed by a lightning strike 15 minutes later.</p>
<p>The work resulted in just three atoms of the new element, each of which lasted for about 1000th of a second. Registering these atoms is just as difficult: a sophisticated detector system is need to pick up the cascade of radioactive decays which end with the atomic nucleus blowing itself apart.</p>
<h2>Why the search for new elements?</h2>
<p>All of which begs the question: why bother? After all, it’s hard to come up with a practical use for an element that takes so much effort to produce and lasts for so short a time.</p>
<p>Studying these super-heavy elements can teach us not only about the forces involved in atomic nuclei, but perhaps surprisingly, also about what goes on when stars die. </p>
<p>When a massive star explodes as a supernova, the extreme conditions could be just right for producing super-heavy elements. There are theoretical hints that some of these elements may buck the trend of increasing instability and exist in long-lived forms, an effect known as “<a href="http://www.superheavies.de/english/research_program/highlights_element_117.htm#The%20island%20of%20stability">the island of stability</a>”.</p>
<p>Current earth-bound experiments are just probing the shores of this island, but will help us determine whether these super-heavy elements could already be present in the universe. Searches in terrestrial rocks and in debris from space have so far drawn a blank, but researchers continue to hunt.</p>
<p>The four new additions to the periodic table have only temporary names at the moment. Rights for naming them go to the discoverers, although the IUPAC imposes strict rules.</p>
<p>Japonium has been suggested as a candidate for element 113, which would make it the first element starting with J. Now if scientists can just come up with a good name starting with Q, the periodic table would be alphabetically complete.</p><img src="https://counter.theconversation.com/content/52862/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Tickner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>New elements found in the reactions of nuclear tests during World War II sparked the hunt for additions to the periodic table.James Tickner, Team Leader, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/527472016-01-05T05:58:20Z2016-01-05T05:58:20ZThe race to find even more new elements to add to the periodic table<figure><img src="https://images.theconversation.com/files/107236/original/image-20160105-28994-t3don9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The expanding periodic table of elements.</span> <span class="attribution"><span class="source">Shutterstock/Olivier Le Queinec</span></span></figcaption></figure><p>In an event likely never to be repeated, four new superheavy elements were last week <em>simultaneously</em> added to the periodic table. To add four in one go is quite an achievement but the race to find more is ongoing.</p>
<p>Back in 2012, the International Unions of Pure and Applied Chemistry (<a href="http://www.iupac.org/">IUPAC</a>) and Pure and Applied Physics (<a href="http://iupap.org/">IUPAP</a>) tasked five independent scientists to assess claims made for the discovery of elements 113, 115, 117 and 118. The measurements had been made at Nuclear Physics Accelerator laboratories in Russia (Dubna) and Japan (RIKEN) between 2004 and 2012. </p>
<p>Late last year, on December 30, 2015, IUPAC <a href="http://www.iupac.org/news/news-detail/article/discovery-and-assignment-of-elements-with-atomic-numbers-113-115-117-and-118.html">announced</a> that claims for the discovery of <em>all four</em> new elements had been accepted. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/30569/original/47ybnrd5-1378164128.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The completed seventh row in the periodic table.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>This completes the seventh row of the periodic table, and means that all elements between hydrogen (having only one proton in its nucleus) and element 118 (having 118 protons) are now officially discovered.</p>
<p>After the excitement of the discovery, the scientists now have the naming rights. The Japanese team will suggest the name for element 113. The joint Russian/US teams will make suggestions for elements 115, 117 and 118. These names will be assessed by IUPAC, and once approved, will become the new names that scientists and students will have to remember.</p>
<p>Until their discovery and naming, all superheavy elements (up to 999!) have been assigned temporary names by the IUPAC. Element 113 is known as ununtrium (Uut), 115 is ununpentium (Uup), 117 is ununseptium (Uus) and 118 ununoctium (Uuo). These names are not actually used by physicists, who instead refer to them as “element 118”, for example.</p>
<h2>The superheavy elements</h2>
<p>Elements heavier than Rutherfordium (element 104) are referred to as superheavy. They are not found in nature, because they undergo radioactive decay to lighter elements.</p>
<p>Those superheavy nuclei that have been created artificially have decay lifetimes between nanoseconds and minutes. But longer-lived (more neutron-rich) superheavy nuclei are expected to be situated at the centre of the so-called “<a href="http://www.superheavies.de/english/research_program/highlights_element_117.htm#The%20island%20of%20stability">island of stability</a>”, a place where neutron-rich nuclei with extremely long half-lives should exist.</p>
<p>Currently, the isotopes of new elements that have been discovered are on the “shore” of this island, since we cannot yet reach the centre. </p>
<h2>How were these new elements created on Earth?</h2>
<p>Atoms of superheavy elements are made by nuclear fusion. Imagine touching two droplets of water – they will “snap together” because of surface tension to form a combined larger droplet. </p>
<p>The problem in the fusion of heavy nuclei is the large numbers of protons in both nuclei. This creates an intense repulsive electric field. A heavy-ion accelerator must be used to overcome this repulsion, by colliding the two nuclei and allowing the nuclear surfaces to touch. </p>
<p>This is not sufficient, as the two touching spheroidal nuclei must change their shape to form a compact single droplet of nuclear matter – the superheavy nucleus.</p>
<p>It turns out that this only happens in a few “lucky” collisions, as few as one in a million.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YovAFlzFtzg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Superheavy reaction fails to fuse (ANU)</span></figcaption>
</figure>
<p>There is yet another hurdle; the superheavy nucleus is very likely to decay almost immediately by fission. Again, as few as one in a million survives to become a superheavy atom, identified by its unique radioactive decay. </p>
<p>The process of superheavy element creation and identification thus requires large-scale accelerator facilities, sophisticated magnetic separators, efficient detectors and <em>time</em>. </p>
<p>Finding the three atoms of element 113 in Japan took 10 years, and that was <em>after</em> the experimental equipment had been developed.</p>
<p>The payback from the discovery of these new elements comes in improving models of the atomic nucleus (with applications in nuclear medicine and in element formation in the universe) and testing our understanding of atomic relativistic effects (of increasing importance in the chemical properties of the heavy elements). It also helps in improving our understanding of complex and irreversible interactions of quantum systems in general.</p>
<h2>The Australian connection in the race to make more elements</h2>
<p>The race is now on to produce elements 119 and 120. The projectile nucleus Calcium-48 (Ca-48) – successfully used to form the newly accepted elements – has too few protons, and no target nuclei with more protons are currently available. The question is, which heavier projectile nucleus is the best to use. </p>
<p>To investigate this, the leader and team members of the German superheavy element research group, based in Darmstadt and Mainz, recently travelled to the Australian National University.</p>
<p>They made use of unique ANU <a href="http://physics.anu.edu.au/nuclear/hiaf.php">experimental capabilities</a>, supported by the Australian Government’s <a href="https://www.education.gov.au/national-collaborative-research-infrastructure-strategy-ncris">NCRIS program</a>, to measure fission characteristics for several nuclear reactions forming element 120. The results will guide future experiments in <a href="http://www-win.gsi.de/tasca/Default.htm">Germany</a> to form the new superheavy elements.</p>
<p>It seems certain that by using similar nuclear fusion reactions, proceeding beyond element 118 will be more difficult than reaching it. But that was the feeling after the discovery of element 112, first observed in 1996. And yet a new approach using Ca-48 projectiles allowed another six elements to be discovered. </p>
<p>Nuclear physicists are already exploring different types of nuclear reaction to produce superheavies, and some promising results have already been achieved. Nevertheless, it would need a huge breakthrough to see four new nuclei added to the periodic table at once, as we have just seen.</p><img src="https://counter.theconversation.com/content/52747/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Hinde receives funding from the Australian Research Council.</span></em></p>They might only last for a fraction of a second but four new elements have finally won their place in the periodic table. The hunt is now on to find even more.David Hinde, Director, Heavy Ion Accelerator Facility, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/471542015-10-14T09:02:12Z2015-10-14T09:02:12ZCan’t take the heat? We need a universal measure on temperature<figure><img src="https://images.theconversation.com/files/95314/original/image-20150918-12351-3bfjdk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A measure of temperature here may be different to elsewhere.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/johnsyweb/2151563670/">Flickr/Pete Johns</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Which weighs more: a kilo of cheese or a kilo of Vegemite? Surprisingly, the answer depends on where they come from.</p>
<p>The science of measurement has a communications problem: how do people agree on how much they are talking about? </p>
<p>Historically, things were measured by convenient but variable references, such as the width of a thumb (an inch) or a foot (a foot) – no doubt responsible for many an <a href="https://vimeo.com/94459739">ancient argument</a>.</p>
<p>Resolving the ambiguity inherent in these rough rules of thumb became important enough to medieval commerce that the <a href="http://www.bl.uk/magna-carta/articles/magna-carta-english-translation">Magna Carta</a> – apparently catering to inebriated textile workers, and now celebrating its 800th year – required that:</p>
<blockquote>
<p>(35) There shall be standard measures of wine, ale, and corn (the London quarter), throughout the kingdom. There shall also be a standard width of dyed cloth, russet, and haberject, namely two ells within the selvedges. Weights are to be standardised similarly.</p>
</blockquote>
<p>During the scientific and industrial revolutions, increasing demands for precision and standardisation in science, mass-production and global commerce lead to the development of the metric system, based on units like the metre, kilogram and second.</p>
<p>This system became the bedrock for the modern scientific edifice, enabling people to quantitatively study phenomena such as gravity, electricity or temperature, for which there are no convenient, everyday references.</p>
<h2>A reference to measure</h2>
<p>Standard units were originally defined by a reference artefact. For instance, a platinum mass in Paris defines the <a href="http://www.bipm.org/en/bipm/mass/prototype.html">primary kilogram</a>, with derivative secondary copies stored in various <a href="http://www.measurement.gov.au/Services/calibrationtesting/Pages/Massandrelatedquantities.aspx#">National Measurement Institutes</a>. </p>
<p>But there remains the problem of reliably distributing the standard. For example, when primary and secondary kilogram masses are periodically compared, they differ slightly. Since National Measurement labs legally define measures within their <a href="http://www.bipm.org/en/publications/si-brochure/chapter1.html">jurisdiction</a>, a kilo of French cheese is currently a <a href="http://www.bipm.org/utils/common/pdf/final_reports/M/M-K1/CCM.M-K1.pdf">microgram lighter</a> than a kilo of Australian Vegemite!</p>
<p>To fix this problem, scientists have been working to redefine the system of units in terms of universal constants, such as the speed of light, the frequency of certain atoms, or the electrical resistance of quantum devices. This program is more or less complete for <a href="http://www.bipm.org/en/publications/si-brochure/second.html">time</a>, <a href="http://www.bipm.org/en/publications/si-brochure/metre.html">length</a> and <a href="http://www.bipm.org/en/publications/si-brochure/ampere.html">electrical charge</a>.</p>
<p>Others, such as mass and temperature, still rely on artefacts. The <a href="http://www.bipm.org/metrology/thermometry/units.html">Kelvin</a> unit for temperature is defined in terms of “<a href="https://nucleus.iaea.org/rpst/referenceproducts/referencematerials/Stable_Isotopes/2H18O-water-samples/VSMOW2.htm">Vienna Standard Mean Ocean Water</a>”, specially prepared by the International Atomic Energy Agency. In the current <a href="http://www.bipm.org/utils/common/pdf/its-90/ITS-90_metrologia.pdf">ITS-90</a> temperature scale, the triple-point (where liquid, solid and gas phases coexist) of this peculiarly named water defines exactly 273.16 Kelvin (0.01°C).</p>
<h2>A universal measure of temperature</h2>
<p>Internationally, there are various approaches being pursued to <a href="http://iopscience.iop.org/0026-1394/page/Focus_on_the_Boltzmann_Constant">redefine the Kelvin</a> in terms of universal quantities.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/95359/original/image-20150918-17709-328yku.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Infrared image of a laser probing a Caesium vapour cell.</span>
<span class="attribution"><span class="source">GW Truong.</span></span>
</figcaption>
</figure>
<p>Our approach, published in <a href="http://dx.doi.org/10.1038/ncomms9345">Nature Communications</a>, is based on Doppler spectroscopy of Caesium atoms in a low pressure vapour at room temperature. An example of the <a href="https://theconversation.com/explainer-the-doppler-effect-7475">Doppler effect</a> is the audible change in frequency of a police siren as it passes by.</p>
<p>Atoms in a gas are zipping around, and the higher the temperature, the larger their typical velocity. </p>
<p>Using very precise lasers we were able to measure the Doppler frequency shift of the atomic spectrum, from which we determine the atomic velocities – just like a traffic cop at a speed trap measures vehicle speeds with a Doppler radar gun.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/98049/original/image-20151012-17807-11imhn2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Formula for calculating the temperature.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>From the atomic velocity (<em>v</em>), we calculate the temperature (<em>T</em>) of the gas using the formula (right; <em>m</em> is the atomic mass and <em>k</em> is <a href="http://physics.nist.gov/cgi-bin/cuu/Value?k%7Csearch_for=physchem_in!">Boltzmann’s constant</a>).</p>
<p>Importantly, there are no unknown calibration factors in our technique; we rely only on universal constants such as the atomic mass and the speed of light. So with sufficient technical skill, any lab – whether on Earth or in the Andromeda galaxy – could replicate our experiment; no reference artefacts required. Even better, our approach scales over a large range of temperatures, from well below freezing to the interior of furnaces.</p>
<p>One of the challenges of this technique is that the laser light used to probe the atoms also changes their internal state, even for extremely low power lasers. Just as motorists become agitated after spotting a speed radar, so the atoms in our experiment become excited by the light used to measure them.</p>
<p>The change in the atomic state is small – just one part in 10,000 – but this is large compared to our target accuracy of one part in a million. Fortunately atoms of the same Caesium isotope are all exactly alike, so we can account for these small changes using quantum theory to dramatically improve our measurement performance. </p>
<p>Getting our system of units right is critical: it is the foundation on which science and technology are built. Upgrading the Kelvin definition will require backward compatibility with the current system, and pursuing several different experimental avenues will ensure we get it right.</p>
<p>As with any upgrade, this one will be deemed successful if the public hardly notice the transition. But to those at the cutting edge – whether developing high-temperature materials processing, studying the cosmic microwave background or making ultra-cold quantum gases – basing the Kelvin on universal and fundamental principles will enable the most rigorous tests of the universe.</p><img src="https://counter.theconversation.com/content/47154/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Stace receives funding from the Australian Research Council and the US Department of Commerce National Institute of Standards and Technology. </span></em></p>How do we know that a measure of something in one location can be replicated precisely in another. We already have a universal measure of mass and time, but what about temperture?Thomas Stace, Associate Professor in Physics, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/262862014-05-07T03:57:52Z2014-05-07T03:57:52ZSomething new and superheavy at the periodic table<figure><img src="https://images.theconversation.com/files/47909/original/nqsyf7x2-1399415924.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Element 117 is unofficially named ununseptium which is Latin for 117.</span> <span class="attribution"><a class="source" href="http://www.flickr.com/photos/larrywfu/2027115602">Flickr/Larry</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The hunt for long-lived <a href="https://theconversation.com/modern-day-alchemy-a-recipe-for-a-new-superheavy-element-17598">superheavy elements</a> has taken another leap forward now we’ve confirmed the existence of Element 117, also known as ununseptium.</p>
<p>It was <a href="http://physicsworld.com/cws/article/news/2010/apr/10/new-element-117-discovered">first seen</a> briefly by a team of US and Russian researchers back in 2010. Its existence has now been confirmed by an international team of researchers including myself, with details <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.172501">published</a> this month in the Physical Review of Letters.</p>
<p>The new evidence should set the stage for Element 117 to become the heaviest named element in the periodic table.</p>
<p>The current temporary name indicates that the atom contains 117 protons. For comparison, <a href="http://www.rsc.org/periodic-table/element/92/uranium">uranium</a> is considered the heaviest naturally occurring element, having 92 protons. Its most stable isotope U-238 is radioactive with a half-life of 4.5 billion years, similar to the age of the Earth.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/cma-AjOUplU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An animation of the 2010 discovery of Element 117.</span></figcaption>
</figure>
<p>The name for this new element is sometimes written as ununseptium, which simply means 117 in Latin. This name was proposed by the International Union of Pure and Applied Chemistry (<a href="http://www.iupac.org/">IUPAC</a>) in 1979 as a temporary name – but it’s never used by superheavy element researchers.</p>
<h2>How to make a superheavy element</h2>
<p>Elements beyond 104 are referred to as superheavy, and the most long-lived ones are expected to be situated on a so-called “<a href="http://www.superheavies.de/english/research_program/highlights_element_117.htm#The%20island%20of%20stability">island of stability</a>” where neutron-rich nuclei with extremely long half-lives should exist. Currently, we are exploring the “shore” of this island, since we cannot yet reach the centre of the island.</p>
<p>Superheavy atoms such as Element 117 have not been found in nature but they can be made by nuclear fusion. That involves bringing together the nuclei of smaller atoms that combine to give the right number of protons. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/47802/original/w9y3pgvw-1399270504.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Element 117 was produced when calcium ions hit this target wheel.</span>
<span class="attribution"><a class="source" href="https://www.gsi.de/en/start/news/detailseite/datum/2014/05/02/superschweres-element-117-nachgewiesen.htm">GSI</a></span>
</figcaption>
</figure>
<p>Four atoms of Element 117 were formed by nuclear fusion at the German accelerator laboratory <a href="https://www.gsi.de/en.htm">GSI</a>, where more than ten billion billion rare <a href="http://www.rsc.org/periodic-table/element/20/calcium">calcium-48</a> nuclei (each with 20 protons and 28 neutrons) were fired at a target (pictured right) made of the even rarer isotope <a href="http://www.rsc.org/periodic-table/element/97/berkelium">berkelium-249</a> (having 97 protons and 152 neutrons).</p>
<p>The Bk-249 material was created at the <a href="http://www.ornl.gov/user-facilities/hfir">High Flux Isotope Reactor</a>, at Oak Ridge in the USA, then shipped to the University of Mainz in Germany, where the expertise existed to make it into the thin target. The Bk-249 has a half-life of only 330 days, so the experiment had to be done quickly.</p>
<p>In the experiment, atoms of Element 117 were separated from huge numbers of other nuclear reaction products in the TransActinide Separator and Chemistry Apparatus (<a href="http://www-win.gsi.de/tasca/Default.htm">TASCA</a>) and were identified through their radioactive decay which occurred in less than a tenth of a second.</p>
<p>The observed chains of alpha-decays produced isotopes of the slightly lighter Elements 115 to 103, whose observation and identification provided proof that Element 117 had indeed been produced.</p>
<h2>The difficulty of making such elements</h2>
<p>There is a huge problem in forming atoms of superheavy elements, not least the extremely low probability of fusion of the two nuclei which are smashed together.</p>
<p>Instead of fusing, the two nuclei usually stick together for a while, maybe one hundredth of a billion billionth (10<sup>-20</sup>) of a second, then come apart. The longer they stick, the better the chance of forming an atom of the new superheavy element.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YovAFlzFtzg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Superheavy reaction fails to fuse (ANU).</span></figcaption>
</figure>
<p>The research team at the Australian National University <a href="http://physics.anu.edu.au/nuclear/hiaf.php">Heavy Ion Accelerator Facility</a> has developed a unique capability to investigate how long two nuclei stick together in the nuclear fusion reactions used to attempt to create superheavy elements.</p>
<p>With the challenge of forming even heavier elements in mind, a couple of years ago the German team leaders invited the ANU group to join their collaboration, to carry out focused measurements to help choose the best nuclear fusion reactions.</p>
<p>Already two collaborative experiments (investigating indications of different fusion behaviour from isotopes of sulphur and titanium) have taken place at ANU.</p>
<p>Preparations at the ANU and in Germany are currently underway to extend the measurements towards the reactions that might be the most favourable to create superheavies up to Element 120.</p>
<h2>All we need is some magic</h2>
<p>The creation of superheavy elements, and the measurement of their properties, contributes to a wide range of associated fields including quantum and nuclear physics, astrophysics and chemistry.</p>
<p>Neutrons and protons exist in quantum energy levels in the nucleus, in a similar way to the quantum energy levels of electrons in atoms. In atoms these lead to the unreactive <a href="http://chemistry.about.com/od/elementgroups/a/noblegases.htm">noble gas</a> elements which have 2, 10, 18, 36, 54 or 86 electrons in total, which all result in closed (full) outer electron shells.</p>
<p>In a similar way, “<a href="http://chemwiki.ucdavis.edu/Physical_Chemistry/Nuclear_Chemistry/Nuclear_Stability_and_Magic_Numbers">magic numbers</a>” of protons and neutrons give additional stability.</p>
<p>Superheavy atoms only exist because their nuclei are more stable than otherwise as a result of these magic numbers. The magic numbers are predicted within different models to be at 114, 120 and 126 protons, while all predict 184 is the magic neutron number.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/47911/original/xdg6bbxf-1399420419.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A view into the 120m long linear accelerator at GSI, which accelerated the calcium ions used to produce Element 117.</span>
<span class="attribution"><a class="source" href="https://www.gsi.de/en/start/news/detailseite/datum/2014/05/02/superschweres-element-117-nachgewiesen.htm">GSI</a></span>
</figcaption>
</figure>
<p>Correctly predicting the masses and decay properties of isotopes of superheavy elements in this region provides a severe test of models of the atomic nucleus, for which the magic numbers are a key component. By testing the models outside their “comfort zone”, they can be refined, or rejected.</p>
<p>These models in turn are used in nuclear astrophysics to describe the nuclear reactions that drive our universe. Element abundances and supernova dynamics are critically dependent on properties of as yet unobserved neutron-rich nuclei. Models are currently the only way to estimate how they behave. </p>
<p>In chemistry, for the heaviest elements the inner electrons are so strongly attracted to the highly charged nucleus that relativistic effects are very important. This affects the chemical properties of the elements, so measuring the chemical properties, such as achieved for <a href="https://www.gsi.de/en/fs2/start/news/detailseite/datum/2010/06/22/chemisches-element-114-erstmals-bei-gsi-erzeugt.htm">Element 114</a> (discovered in 1999 and known as <a href="http://www.rsc.org/periodic-table/element/114/flerovium">flerovium</a>), tells us how well we understand these relativistic effects.</p>
<p>The fusion process involves transforming two separate many-body quantum systems (the colliding nuclei) into one. The huge repulsion between 117 protons packed into the tiny volume of the superheavy nucleus makes this a very delicate operation.</p>
<p>Detailed quantum properties of the two colliding nuclei seem to affect how easily they can fuse into one, including the presence of magic numbers, and the shapes and relative orientations of the two nuclei. Similar orientation effects have been seen in reaction rates of some molecules.</p>
<p>The ANU group has been working to understand this quantum dynamics, as well as the transition from an initial situation involving quantum probabilities to a definite irreversible outcome. This should be of general relevance to interactions of other many-body quantum systems such as atoms and molecules.</p><img src="https://counter.theconversation.com/content/26286/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Hinde receives funding from the Australian Research Council for research into nuclear reactions forming superheavy elements.</span></em></p>The hunt for long-lived superheavy elements has taken another leap forward now we’ve confirmed the existence of Element 117, also known as ununseptium. It was first seen briefly by a team of US and Russian…David Hinde, Director, Heavy Ion Accelerator Facility, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/80572012-07-04T01:07:47Z2012-07-04T01:07:47ZSnapping an atom’s shadow? Now that’s a first<figure><img src="https://images.theconversation.com/files/12573/original/fz4x8y3k-1341354935.jpg?ixlib=rb-1.1.0&rect=0%2C136%2C512%2C323&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A world-first image with implications for everything from quantum computing to microbiology.</span> <span class="attribution"><span class="source">Kielpinksi Group/Centre for Quantum Dynamics</span></span></figcaption></figure><p>As the image above illustrates, my colleagues and I at Griffith University have been able to photograph the shadow of an atom for the first time – the culmination of five years of work by our team.</p>
<p>The image, and attendant paper, are <a href="http://www.nature.com/ncomms/journal/v3/n7/full/ncomms1944.html">published today</a> in the journal Nature Communications. </p>
<p>So, in a nutshell, how did we get the image? The following analogy might help. </p>
<p>On a sunny day at the beach, your shadow is a constant companion. Holding your hand up will block the bright sun, but a few rays will still penetrate the thinner parts of your fingers. </p>
<p>If we were to take a closer look using a microscope we would see dark strands of tightly wound DNA in the <a href="http://www.els.net/WileyCDA/ElsArticle/refId-a0005975.html">nucleolus</a> (composed of proteins and nucleic acids found within the nucleus) of the skin cells. Looking closer still, we might wonder: how small can something be and still cast a shadow?</p>
<p>The picture leading this article shows the shadow cast in a laser beam by a single <a href="http://www.chemicool.com/elements/ytterbium.html">Ytterbium atom</a> suspended in empty space. At Griffith University, we have has pioneered the use of <a href="http://en.wikipedia.org/wiki/Fresnel_lens">Fresnel lenses</a> (a type of lens for large aperture and short focal length – producing an ultra hi-res miscroscope) to capture high-resolution images of atoms. </p>
<p>Our lens is like a smaller versions of the lenses used in lighthouses – both have many separate segments all working in concert to focus the light.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=527&fit=crop&dpr=1 600w, https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=527&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=527&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=663&fit=crop&dpr=1 754w, https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=663&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/12574/original/gy7wcznz-1341354952.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=663&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Single Atom Shadow Experiment.</span>
<span class="attribution"><span class="source">Kielpinksi Group/Centre for Quantum Dynamics</span></span>
</figcaption>
</figure>
<p>The figure above shows how a laser beam (orange) passing by a single atom (blue) leaves a dark shadow in its wake, with the actual picture of the single atom shadow shown on the right end.</p>
<p>Since a single atom casts a very small shadow, our advances allowed us to be the first to take a picture of this effect. The size of the shadow is set by the wavelength of light, which is about a thousand times larger than the actual atom. </p>
<p>We hold the Ytterbium atom in empty space by removing one of its electrons and using high voltage electricity to fix its position. Ytterbium was chosen because we could build lasers of the right colour to be strongly absorbed by the atom.</p>
<h2>Implications</h2>
<p>Our work has implications for research ranging from <a href="https://theconversation.com/explainer-quantum-physics-570">quantum computing</a> to microbiology. In quantum computing, light is the most effective method for communication, while atoms are often better for performing calculations. </p>
<p>In observing the shadow from a single atom we have shown how to improve the input efficiency in a quantum computer. Single atoms have well-understood light absorption properties. We used this knowledge to predict how dark the shadow should be for a given amount of light.</p>
<p>Since Dutch scientist <a href="http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek">Antonie van Leeuwenhoek</a>’s first observations of <a href="http://en.wikipedia.org/wiki/Red_blood_cell">red blood cells</a> in 1674, <a href="http://www.azonano.com/article.aspx?ArticleID=2890">absorption microscopy</a> has played a prominent role in biology. X-ray and ultraviolet light are very useful for imaging cells but can also damage them at high dosages. </p>
<p>By knowing how much light is required to achieve a particular image quality, our work will be useful to predict when a little damaging light is enough to take a good image.</p>
<p>We’re pleased to be the first to capture a snap of the long shadow from an single atom’s dark side.</p><img src="https://counter.theconversation.com/content/8057/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Erik Streed receives research funding from the Australian Research Council. He is presently a Lecturer in Physics at Griffith University's Gold Coast campus.</span></em></p>As the image above illustrates, my colleagues and I at Griffith University have been able to photograph the shadow of an atom for the first time – the culmination of five years of work by our team. The…Erik Streed, Lecturer in Physics, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.