Sealed sources

Sealed sources are radioactive sources containing radioactive material that has been encapsulated in a solid, impenetrable capsule, preventing the radioactive material from spreading to its surroundings. From a sealed source the radioactive material does not spread to the surrounding environment provided that the sealed source is maintained accordingly.

The properties of sealed sources, and hence their use cases, vary depending on what radionuclide and activity the sealed source contains. The most commonly used sealed sources are made of cobalt-60 radionuclide or cesium-137 radionuclide, which both emit gamma rays. Other typically used sealed sources are made of the beta decaying radionuclides like krypton-85 or strontium-90 as well as the alpha decaying americium-241.

In industry sealed sources can be used in a variety of applications: as a gauge for measuring the fill level of a substance, the density of material or even the moisture content of soil. In healthcare sealed sources are used as test sources to check the performance of imaging devices and radiation detectors.

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Sealed sources are reliable and require little maintenance since the sealed source does not require an external power supply. The radiation produced by a sealed source has uniform intensity and changes only steadily due to the radioactive decay process. It is important to take care of the environmental conditions and other external factors to make sure these do not damage the protective casing or the capsule of the sealed source. The condition of a sealed source should be monitored regularly by performing visual inspections and leakage testing. Attention should be paid for example to the condition of the cover, the warning labels and the operation of the shutter of the sealed source device. In particular, when the sealed source has been in use for a long time, its condition should be monitored rigorously.