gamma-rays
Last reviewed 01/2018
Gamma-rays are used as a type of megavoltage irradiation, with cobolt 60, a radioactive isotope of cobolt 59, being the principle source in medicine.
The source requires replacement every 3 years, and during its useful life it produces a 1.2 MeV beam.
Caesium 137 is used in a similar way in other units.
Gamma rays are a result of nuclear decay, where binding energy is emitted as electromagnetic radiation.
The peak intensity of the radiation is at a depth of 5mm, after which there is decay. The surface gets 50% of maximum intensity dose.