Long term activation in a 15 MeV radiotherapy accelerator

Abstract

The high energy electrons produced by linear accelerators can generate several radioisotopes by means of photonuclear reactions. The activity produced in the head of a 15 MV Mevatron Siemens 77 medical linear accelerator was measured by high resolution gamma-ray spectrometry, during its decommissioning 1 year after the last clinical use. The activity of 54Mn, 57Co, 60Co, 181W, and 65Zn was measured while the activity of other radioisotopes which emit soft beta or gamma rays such as 59Ni, 63Ni, and 55Fe was inferred by appropriate scaling factors. The number of pieces requiring particular care is limited, their mass does not exceed some tens of kilograms, and their volume is of the order of some thousands of cm3. Moreover, these materials are metals and the emitted radiation can be easily shielded, so that storage should not create particular problems.