Nuclear technology is used in medicine to locate and study diseased tissue using special drugs called radiopharmaceuticals. Radioactive tags are used to identify cancer cells in the bones, brain tumors, and Alzheimer’s disease, and to monitor the function of body organs, such as blood flow, heart muscle activity, and iodine uptake in the thyroid gland.

The biological effects of ionizing radiation are due to two effects it has on cells: interference with cell reproduction and destruction of cell function.

Common sources of radiation include that emitted by Earth due to the isotopes of uranium, thorium, and potassium; natural radiation from cosmic rays, soils, and building materials, and artificial sources from medical and dental diagnostic tests.

The biological effects of nuclear radiation are expressed by many different physical quantities and in many different units, including the rad or radiation dose unit.