Radioactive sources are worldwide used for a high variety of productive and peaceful purposes in medicine, research, education and industry. These sources utilize radioactivematerials that are firmly contained or bound within a suitable capsule or housing; although some sources involve radioactive materials in an unsealed form.
Up to the 1950s, only radionuclides of natural origin were generally available for sources. Since then, radionuclides produced artificially in nuclear facilities and accelerators have become widely available. Radioactive sources vary widely in physical size and properties, the amount of radiation they emit, and type of encasing. Some are portable instruments, such as gauges for taking measurements, while others are fixed pieces of equipment, such as a radiotherapy machine for cancer treatment.