346. “Day after” high energy linear accelerator decomissioning: Characterization of the head of the accelerator

Abstract

Purpose Italian laws are very restrictive in terms of release and exemption quantities in case of waste contaminated by radioactive isotopes. This study focuses on the characterization of a 18 MV Elekta Precise Linear Accelerator head that have been in clinical use since two days before its dismantling to make space to a new “state of the art” machine. Methods Dismantling have been carried out by an Italian specialized company, each part of the machine have been first measured with a high efficiency α, β, γ contamination monitor equipped with ZnS:Ag detector and a portable γ-ray spectrometer (NaI(Tl)). Activated parts have been subsequently measured with a low background, high reliability and high definition spectrometric chain (DSA-1000 and Genie 2000 software, Canberra), with an electric cooled High Purity Germanium detector (HPGe) with 20% relative efficiency (GX2018 detector and Cryo-Pulse5 plus cooler, Canberra). Energy, FWHM and efficiency calibration have been performed with a multigamma Marinelli source in the range 59 keV (241 Am) – 1836 keV (88Y). Efficiency curves for different geometries have been calculated with a 3D model of the detector-sample system and Montecarlo (MC) method by ISOCS/LabSOCS efficiency software (Canberra). Results 57Co, 58Co, 60Co, 54Mn have been among the more frequent radioisotopes found. However short lived nuclides (eg. 122Sb, 187W, 57Ni) were present as well. Conclusions Activation of long lived radionuclides was confirmed as previously reported in published paper [1] , [2] ; short lived radionuclides were detected as well. Waiting for full decay of short lived radioisotopes could allow to minimize the amount of radioactive waste. Download : Download high-res image (99KB) Download : Download full-size image