X-rays are like light rays, but they can pass through more stuff. Some of the x-ray’s energy is blocked by bone, which is why you can see bones so clearly on x-ray scans.
Marie Curie in one of her mobile X-ray units in October 1917.
Eve Curie
During World War I, Marie Curie left her lab behind, inventing a mobile X-ray unit that could travel to the battlefront and training 150 women to operate these ‘Little Curies.’