DETERMINATION OF ACTIVATION PRODUCTS AND RESULTING DECOMMISSIONING IMPLICATIONS FOR THE VARIAN TRUEBEAM LINEAR ACCELERATOR

摘要

Medical linear accelerators used to treat various forms of cancers are operated at a number of different energies. A by-product of the high-energy photons produced by accelerators is activation of components within the machine itself and its surrounding bunker. The activation products pose radiological and regulatory challenges during the operation of the accelerator as well as when it is time for final decommissioning. The Varian TrueBeam is a new state-of-the-art linear accelerator now operating in the Canadian market. There is currently limited information on the production of its activation products and the resulting impacts on operation and decommissioning. In this paper, the activation products in the Varian TrueBeam accelerator are experimentally determined by performing gamma spectroscopy using a portable high purity germanium detector. A total of 11 isotopes are identified which includes ~(24)Na, ~(28)Al, ~(56)Mn, ~(57)Ni, ~(64)Cu, ~(66)Cu, ~(85)Br, ~(122)Sb, ~(124)Sb, ~(187)W, and ~(228)Ac. The half-lives of these isotopes range from 2.3 minutes to 60.2 days. Combining the CNSC isotope exemption quantities found in the Canadian Nuclear Substance and Radiation Device regulations and the isotopic quantities determined during the gamma spectroscopy, the aggregate exemption quantity for the accelerator at any given time is determined. After 36 hours, a decommissioning case can be presented to the CNSC for the disposal of the accelerator or shipment to a non-licensee in the USA.