Abstract During the operational life of a PET cyclotron, the concrete walls of the vault are activated by secondary neutrons. For the dismantling of such accelerator facilities, a considerable amount of low level solid radioactive waste has to be characterized and disposed. To decrease future dismantling costs and complexity, the amount of radioactive waste has to been prospectively evaluated in the design phase, then confirmed at the time of planning decommissioning. In this work, the Monte Carlo code Fluka was used for the assessment of the activation of the bunkers of two different facilities: the 16.5 MeV GE PETtrace at S. Orsola-Malpighi Hospital in Bologna and the 18 MeV IBA Cyclone 18/18 HC at the Bern University Hospital (Inselspital). The simulations were validated by means of experimental measurements performed in our previous works: non-destructive, in field measurements using a portable CZT detector were performed in Bologna; while core drilling samples were extracted from the bunker and measured in laboratory with an HPGe detector in Bern. The activity of the most important radionuclides in the concrete walls of the bunker, namely Eu-152, Mn-54, Co-60, Sc-46, Zn-65 and Cs-134 resulted within the range of 0.01 – 2 Bq/g. The consistency between Monte Carlo results and experimental measurements was within a factor 2 - 3 for most radionuclides, except for Eu-152, Sc-46, Zn-65. The activity concentrations estimated at each position considered exceeds the clearance levels of the new Directive 2013/59/Euratom. The results of this work demonstrate that Monte Carlo simulations based on FLUKA are adequate to assess the residual activation levels, a fundamental information to foresee, plan and optimize the decommissioning of a cyclotron based PET centers.

中文翻译：

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通过蒙特卡罗模拟对 PET 回旋加速器掩体退役的活化研究

摘要 在 PET 回旋加速器的使用寿命期间，拱顶的混凝土墙被二次中子激活。为了拆除此类加速器设施，必须对大量低放固体放射性废物进行表征和处置。为了降低未来的拆除成本和复杂性，必须在设计阶段对放射性废物的数量进行前瞻性评估，然后在计划退役时进行确认。在这项工作中，蒙特卡罗代码 Fluka 用于评估两个不同设施的地堡的激活：博洛尼亚 S. Orsola-Malpighi 医院的 16.5 MeV GE PETtrace 和位于博洛尼亚的 18 MeV IBA Cyclone 18/18 HC伯尔尼大学医院（Inselspital）。通过我们之前工作中进行的实验测量来验证模拟：使用便携式 CZT 探测器在博洛尼亚进行了无损现场测量；同时从掩体中提取岩心钻孔样品并在伯尔尼的实验室中使用 HPGe 探测器进行测量。掩体混凝土墙中最重要的放射性核素，即 Eu-152、Mn-54、Co-60、Sc-46、Zn-65 和 Cs-134 的活性在 0.01 – 2 Bq/g 的范围内. 对于大多数放射性核素，除了 Eu-152、Sc-46、Zn-65 之外，蒙特卡罗结果与实验测量结果之间的一致性在 2-3 倍之内。在考虑的每个位置估计的活动浓度超过了新指令 2013/59/Euratom 的清除水平。这项工作的结果表明，基于 FLUKA 的蒙特卡罗模拟足以评估剩余激活水平，这是一个可预见的基本信息，