Maureen McQueen CRadP MSRP has over 30 years ' experience of almost all applications involving radiation in both the nuclear and non-nuclear sectors . In this article she outlines the main types and applications of radioactive sources .

Radioactive sources are man-made sources of radiation produced by the irradiation of materials in nuclear reactors or linear accelerators for use in industry , medicine , calibration or testing . They fall into two categories :

• Unsealed sources , where the radioactive material is a liquid or a powder inside a container or plated onto a material . If the container is opened or the surface is damaged , the radioactive material inside can escape and cause contamination .

• Sealed sources , where the radioactive material has either been anodised into a surface or encapsulated inside a robust container which will prevent the radioactive material from being released to the environment . In this form the source material , while physically contained , remains usable for its radioactive properties , e . g . the emission of beta , gamma or neutron radiations .

Unsealed Sources Unsealed sources of radiation are commonly used in the medical sector . Technetium-99m , a 140 keV gamma emitter , is used in quantities up to about 1 GBq in nuclear medicine departments for the diagnostic imaging of conditions such as injuries , infections and diseases . A chemical containing Tc-99m is injected into patients where it is concentrated by the metabolism into the target organ or tissue . The radiation which is emitted is then viewed using a gamma camera to produce a detailed image which is interpreted by medical staff . Because the half-life of Tc-99m is only 6

hours , the radioactivity is quickly eliminated from the patient ' s body after imaging .

For therapeutic purposes , Iodine-131 is used in up to GBq quantities in capsule form to target and destroy thyroid tissue as part of cancer treatment . Because excretion of the I-131 results in unsealed radioactive material being released from the body in saliva , sweat and urine , the patient must be appropriately managed after treatment to avoid exposing others to radiation .

Technetium-99m injection Unsealed sources are used in life science research where they are usually handled in very small quantities ( up to tens of MBq ) in research applications in hospital , university and pharmaceutical laboratories . Liquids containing radionuclides are also used in small quantities as calibration sources for laboratory equipment .

Sealed Sources Sealed sources are used for a wide range of industrial and medical applications , ranging from simple calibration sources for the calibration and testing of radiation detection equipment ( e . g . button sources ) to more robust sealed sources containing higher activities of radioisotopes in which a metal container is typically welded around the radioactive material . This may be double or triple encapsulated , and ensures that the radioactive material cannot escape .

Brachytherapy ( internal radiotherapy ) is an example of the medical use of encapsulated sources . Low dose brachytherapy involves the surgical implantation of small sealed

12 Radiation Protection Today www . srp-rpt . uk