Development of a personal dosimeter applied for the photon and fast-neutron fields in high-energy accelerator facilities

1. 作为开发适用于快中子（能量bbb10 MeV）的个人剂量计的第一步，我们测试了使用双层CR-39堆（0.9 mm厚度x 2）测量由0.25,0.55,5和15 MeV的快中子引起的二次带电粒子的LET分布的可行性。探测器的前几层充当散热器，后几层充当中子探测器。结果表明：对于亚MeV中子，需要小于5um的化学刻蚀才能得到正确的LET分布和剂量；现有的CR-39探测器系统和化学蚀刻条件（体蚀刻~15 μm）适合于5 MeV中子剂量测定，LET > 10 keV/μm的剂量当量和平均质量因子分别符合ICRP 74中子辐照剂量转换因子和ICRP 60辐射加权因子；15mev中子剂量测定需要~ 2mm厚的辐射体。虽然目前的测量部分未能得到快中子诱导的低能和短程带电粒子的正确LET值，但我们认为，CR-39探测器系统和化学刻蚀条件的改进应提高快中子剂量学在亚MeV至数十MeV能量范围内LET分布测量的准确性。研制了一种自动扫描系统，用于测量大量的核轨迹腐蚀探测器。研究了高能重离子和快中子辐照CR-39塑料样品的扫描性能。包括样品转移、样品ID识别、图像采集和图像分析在内的整体扫描速度令人满意地高。该系统允许在一天内处理100个样品，扫描面积为4 cm2/样品。开发了一种用于个人剂量测定的新软件“LETDose”。该软件结合了tld测量的吸收剂量和CR-39跟踪探测器测量的LET分布，用于估计由光子和快中子组成的辐射场的吸收剂量和剂量当量。少

1. As a first step toward developing a personal dosimeter applicable for fast neutrons (energy > 10 MeV), we tested the feasibility of using two-layer CR-39 stacks (0.9 mm in thickness x 2) to make LET distribution measurements for secondary charged particles due to fast neutrons of 0.25, 0.55, 5 and 15 MeV. The front layers of the detectors act as a radiator and the back layers act as a neutron detector. The results indicated the following: chemical etching shorter than 5 um is needed to obtain the correct LET distribution and dose for sub MeV neutrons; the present CR-39 detector system and chemical etching condition (bulk etch ~15 μm) are appropriate for 5 MeV neutron dosimetry, and measured dose equivalents and averaged quality factors for LET > 10 keV/μm agreed with the ICRP 74 neutron-fluence-to-dose conversion factor and the ICRP 60 radiation weighting factor, respectively; a thick radiator of ~2 mm is required for 15 MeV neutron dosimetry. Although the present measurements partl … More y failed to obtain correct LET values for the low-energy and short-range charged particles induced by fast neutrons, we conclude that modifications of the CR-39 detector system and chemical etching condition should improve the accuracy of LET distribution measurement for fast neutron dosimetry in the sub MeV to tens MeV energy range.2. An automated scanning system was developed for measuring a large number of nuclear track-etch detectors. We investigated scanning performance using CR-39 plastic samples irradiated by high-energy heavy ions and fast neutrons. Overall scanning speed including sample transfer, sample ID recognition, image acquisition and image analysis was satisfactorily high. The system allowed the processing of 100 samples with scan areas of 4 cm2/sample in one day for neutron dosimetry.3. A new software "LETDose" was developed for personal dosimetry. The software combines absorbed doses measured by TLDs and the LET distributions measured by CR-39 track detectors for estimating absorbed doses and dose equivalents for radiation fields consisting of photons and fast neutrons. Less