There are a great many medical uses of Radioactivity.

The two main categories of use are


Nuclear medicine is where radioactive substances are used for diagnosis or for therapy.

Technetium-99 is radioactive with a half life of 6 hours.

Technetium-99 emits gamma rays which are detected by a gamma camera.

Personnel exposed to radiation are carefully monitored.

Radioactivity in Medicine

Ionising radiation has two very different uses in medicine: diagnosis and therapy. Both benefit the patient but, as with the use of any form of radiation, the benefit must outweigh the risk to justify its use. X-ray examination uses a low level of ionizing. Much higher doses are required to treat malignant diseases or malfunctioning organs, sometimes in combination with other forms of treatment. The use of X-rays for examining patients is called diagnostic radiology and the use of radionuclides for diagnosis or therapy is called nuclear medicine. When radiation beams are used to treat patients, the procedure is called radiotherapy.

Nuclear Medicine

For a diagnostic procedure in nuclear medicine, the patient is given a radionuclide in a carrying substance, such as a pharmaceutical. In some cases the patient inhales the substance; in others it may be swallowed or injected. Once the radionuclide is inside the body, it is absorbed by the tissue or organ under study. The radionuclide emits gamma rays. Most of the diagnostic procedures make use of the radionuclide Technetium-99 (which has a half-life of 6 hours, gives off gamma rays with an energy of 0.14 MeV and can be conveniently prepared in a hospital). A special detector called a gamma ray camera is used to observe how the organs or tissue behave or how quickly the radionuclide moves.

Detectors and Imagers

The gamma camera consists of a large disc of sodium iodide, which emits flashes of light when struck by gamma rays. The disc is typically 40 cm in diameter and 1 cm thick. Photomultiplier tubes are attached to the disc and are arranged in a specific pattern. These tubes receive signals from each flash of light in the crystal. Because they are at different distances from it, the intensity will differ. This difference enables the coordinates of each flash to be determined and, with the aid of many flashes from different parts of the organ under study, enables an image to be reconstructed. The isotope most commonly used is Technetium–99 which has a photon energy of 140 keV. Gamma cameras are used in hospitals to detect the position of radioactive tracers (e.g. Technetium-99) injected in to the patient’s bloodstream. This helps in the diagnosis of a wide range of illnesses.

Thermoluminescent dosimeter

Thermoluminescent dosimeters (TLDs) are devices that are replacing film badges for monitoring personnel, and are also used for monitoring patients’ doses during therapy and for calibrating radiation sources in hospitals. TLDs are inexpensive and can be made very small to measure exposure within the body at sites such as tumours.

More Information

Frequently asked questions on health