Rays or radiation of extremely short wave length (shorter than ultraviolet
radiation). X-rays can penetrate matter that light cannot,
so x-ray cameras can be used to see structures inside the body
that are not normally visible. This is widely used in diagnosis.
Exposure to x-rays must be carefully controlled, as they are harmful
to living cells. This,
however, also makes them useful in treating cancer,
where they are used in larger quantities to destroy cancer cells
within the body (see radiotherapy).
