X-rays were discovered accidentally in 1895 by Wilhelm Conrad Roentgen, a German physicist, when a fluorescent screen in his lab glowed during nearby experiments with electron beams. On putting his hand between the cathode ray tube and the fluorescent screen he discovered he could see an image of his bones. Roentgen called this never before seen radiation X-rays because he did not know what he had discovered. Nowadays, X-rays are known to be a form of highly energetic electromagnetic radiation.
How does it work?
The wave length of X-rays is roughly the same size as atoms. Being so small they penetrate right through the body. After passing through the part of the body being imaged, the X-rays arrive at the photographic plate. The different images produced on the plate are due to the different X ray absorption rates of the different body tissues. Calcium in bones absorbs X-rays the most, so bones look white on a film recording of the X-ray image. Fat and other soft tissues absorb less, and look gray. Air absorbs the least, so lungs look black on a radiograph.
Is medicine the only application of the X-rays?
No, X-ray images are also useful in scientific research. By using this technique scientists are able to determine the 3-dimensional structure of some molecules. This is important, for example, in order to design new medicines.
Scanning for medical purposes: PET scanners