But physicians also use X rays to treat cancer. X rays kill cancer cells more readily than they kill normal cells. In X-ray machines used in medicine and science, a special tube that resembles a television picture tube produces X rays. Scientists also use intense, narrow beams of X rays generated by devices called synchrotrons. Radiographs help physicians detect injuries and diseases, such as broken bones or tumors, inside a patient's body.
Dentists take X-ray pictures to reveal cavities in teeth.
Because X rays can harm living tissue, health workers who use them in diagnostic work give their patients only as much radiation as necessary. In addition, the workers shield parts of the body not being examined. For example, a dental technician lays a lead apron on a patient's body before taking X rays of the patient's teeth. A health worker produces a radiograph by passing a beam of X rays through the patient's body onto a sheet of photographic film or a special plastic that is sensitive to X rays. The patient's bones absorb more rays than do the muscles or internal organs, and so the bones cast the sharpest shadows on the film or plastic.