A radioactive isotope. An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation. More that 1300 natural and artificial radioisotopes have been identified.

The radioactive form of an element that has all the chemical properties of the stable form of the element is a radioisotope. The radioisotope undergoes radioactive decay.

A radioactive form of an element. Used in certain diagnostic tests.

a type of atom that is unstable and prone to break up (decay). Decay releases small fragments of atoms and energy. Exposure to certain radioisotopes can cause cancer. But radioisotopes are also used to find and treat cancer. In certain imaging procedures, for example, radioisotopes are injected into the body where they then collect in areas where the disease is active, showing up as highlighted areas on the images. In breast cancer, radioisotopes are used to check for metastasis to the bones.