Calandrino R, del Vecchio A, Savi A, Todde S, Griffoni V, Brambilla S, Parisi R, Simone G, Fazio F
Health Physics Department, Servizio di Fisica Sanitaria, IRCCS San Raffaele, Via Olgettina 60, 20132 Milan, Italy.
Health Phys. 2006 Jun;90(6):588-96. doi: 10.1097/01.HP.0000190161.96172.ae.
The present article describes the decommissioning of a compact, self-shielded, 11 MeV medical cyclotron. A Monte Carlo simulation of the possible nuclear reactions was performed in order to plan the decommissioning activities. In the course of the cyclotron dismantling, cyclotron components, shields, and floor concrete samples were measured. Residual activities were analyzed with a Ge(Li) detector and compared with simulation data. Doses to staff involved in the decommissioning procedure were monitored by individual TL dosimeters. The simulations identified five radioactive nuclides in shields and floor concrete: 55Fe and 45Ca (beta emitters, total specific activity: 2.29 x 10(4) Bq kg) and 152Eu, 154Eu, 60Co (gamma emitters, total specific activity: 1.62 x 10(3) Bq kg-1). Gamma-ray spectrometry confirmed the presence of gamma emitters, corresponding to a total specific activity of 3.40 x 10(2) Bq kg-1. The presence of the radioisotope 124Sb in the lead contained in the shield structure, corresponding to a simulated specific activity of 9.38 x 10(3) Bq kg-1, was experimentally confirmed. The measured dose from external exposure of the involved staff was <20 muSv, in accordance with the expected range of values between 10 and 20 muSv. The measured dose from intake was negligible. Finally, the decommissioning of the 11 MeV cyclotron does not represent a risk for the involved staff, but due to the presence of long-lived radioisotopes, the cyclotron components are to be treated as low level radioactive waste and stored in an authorized storage area.
本文描述了一台紧凑型、自屏蔽的11兆电子伏医用回旋加速器的退役过程。为了规划退役活动，对可能的核反应进行了蒙特卡罗模拟。在回旋加速器拆除过程中，对回旋加速器部件、屏蔽层和地面混凝土样本进行了测量。用锗锂探测器分析了剩余活度，并与模拟数据进行了比较。参与退役程序的工作人员所受剂量由个人热释光剂量计进行监测。模拟在屏蔽层和地面混凝土中识别出五种放射性核素：55铁和45钙（β发射体，总比活度：2.29×10⁴贝可勒尔/千克）以及152铕、154铕、60钴（γ发射体，总比活度：1.62×10³贝可勒尔/千克⁻¹）。γ射线能谱分析证实了γ发射体的存在，其总比活度为3.40×10²贝可勒尔/千克。实验证实了屏蔽结构中铅内存在放射性同位素124锑，模拟比活度为9.38×10³贝可勒尔/千克。所涉工作人员外部照射的测量剂量<20微希沃特，符合预期的10至20微希沃特值范围。摄入剂量的测量值可忽略不计。最后，11兆电子伏回旋加速器的退役对所涉工作人员不构成风险，但由于存在长寿命放射性同位素，回旋加速器部件应作为低水平放射性废物处理，并存储在经授权的存储区域。
