Martinez-Serrano J Javier, Diez de Los Rios Antonio
*Departamento de Física Aplicada I, Facultad de Ciencias, Boulevar Louis Pasteur s/n, Universidad de Malaga, 29010, Malaga, Spain; †Departamento de Radiología y Medicina Física, Facultad de Medicina, Boulevar Louis Pasteur 32, Universidad de Malaga, 29010, Malaga, Spain.
Health Phys. 2014 Aug;107(2):103-10. doi: 10.1097/HP.0000000000000064.
The PET cyclotron at the Centre of Molecular Imaging of the Universidad de Malaga (CIMES) is a 16.5 MeV GE PETtrace cyclotron working at dual beam (40 μA beam). The cyclotron is dedicated mainly to F production. The F target has two thin circular foils composed of a metal alloy (Havar), that are highly activated by the proton beam and secondary neutrons. The main purpose of this study is to assess induced activity radiological risk derived from the Havar foils activation. Induced activity in Havar foils was estimated by two procedures. One consisted in estimating neutron and proton fluxes with MCNPX and using them as inputs in the activation code ACAB. Alternatively, given the regular periodicity of the irradiation cycles, an analytical expression was derived to estimate activity concentrations of activation products using production rates calculated with MCNPX. Large differences were found in the induced foil activities predicted by the two procedures. Therefore, an irradiated vacuum foil was measured with a Ge detector to analyze activity levels. Cobalt-58 (Co) and Co activities calculated with ACAB match well with measurements. Cobalt-60 (Co) activity estimated with the alternative method agrees acceptably with the measured activity, and Co activity is slightly overestimated. Cobalt-57 (Co) is the activation product of concern in the long term. The vacuum and window foils will be exempted in 3.3 y and 5.5 y, respectively, after replacement. Calculated effective dose with MCNPX and ICRP reference HML phantoms in the foils replacement operation is 0.34 mSv, and annual effective dose would be 2.1 mSv, which is below the annual limits.
马拉加大学分子成像中心（CIMES）的正电子发射断层扫描回旋加速器是一台16.5兆电子伏特的通用电气PETtrace回旋加速器，以双束流（40微安束流）运行。该回旋加速器主要用于生产氟。氟靶有两个由金属合金（哈瓦尔合金）制成的薄圆形箔片，质子束和次级中子会使其高度活化。本研究的主要目的是评估哈瓦尔箔片活化产生的感生放射性风险。通过两种方法估算了哈瓦尔箔片中的感生放射性。一种方法是用MCNPX估算中子和质子通量，并将其作为活化代码ACAB的输入。另外，考虑到辐照周期的规律周期性，推导了一个解析表达式，用MCNPX计算的产率来估算活化产物的活度浓度。两种方法预测的箔片感生活度存在很大差异。因此，用锗探测器测量了一个辐照过的真空箔片，以分析其活度水平。用ACAB计算的钴 - 58（⁵⁸Co）和钴 - 60（⁶⁰Co）活度与测量值吻合良好。用另一种方法估算的钴 - 60（⁶⁰Co）活度与测量活度可以接受地相符，而钴 - 57（⁵⁷Co）活度略有高估。从长期来看，钴 - 57（⁵⁷Co）是需要关注的活化产物。更换后，真空箔片和窗箔片将分别在3.3年和5.5年后豁免。用MCNPX和国际辐射防护委员会（ICRP）参考HML体模计算的箔片更换操作中的有效剂量为0.34毫希沃特，年有效剂量为2.1毫希沃特，低于年剂量限值。
