PDF(Pubmed)
Abstract：
The objective of this paper is to evaluate the accuracy of the NASA BioSentinel Pixel Dosimeter (BPD) using gamma-ray and neutron sources in a standard calibration lab. The dosimeter tested here is the ground-based version of the BPD that will be onboard the BioSentinel mission. The BPD was exposed to radiation from 60Co, 137Cs, and 252Cf at selected distances (dose rates) at the Lawrence Livermore National Laboratory (LLNL) Radiation Calibration Laboratory (RCL), and the results were compared with NIST traceable benchmark values. It is recognized that these sources are not analogs for the space environment but do provide direct comparisons between BPD response and well characterized calibration lab values. For gamma rays, the BPD measured absorbed dose agrees to ≤ 3.8% compared with RCL benchmark values. For neutrons, the results show that the BPD is insensitive, i.e., the BPD detected only the gamma-ray dose component from 252Cf. The LET spectra obtained for gamma rays from 60Co and 252Cf are consistent with expectations for these gamma-ray energies, but the LET spectrum from the 137Cs gamma rays differs substantially. The potential causes for this difference are the high dose rate from 137Cs and the lower secondary electron energy produced by 137Cs gamma rays. However, neither of these results in errors in the absorbed dose. Based on comparisons with NIST-traceable standards, it is evident that the BPD can measure absorbed dose accurately from low LET charged particles. The sensor\'s insensitivity to neutrons is unlikely to be a limitation for the BioSentinel mission due to the expected low secondary neutron fluence.
摘要：
本文的目的是在标准校准实验室中使用伽马射线和中子源评估NASABioSentinel像素剂量计（BPD）的准确性。这里测试的剂量计是BPD的地面版本，将在BioSentinel任务中使用。BPD暴露于60Co的辐射，137Cs,在劳伦斯利弗莫尔国家实验室（LLNL）辐射校准实验室（RCL）的选定距离（剂量率）和252Cf，并将结果与NIST可追溯的基准值进行比较。应当认识到,这些来源不是空间环境的类似物,而是提供了BPD响应和良好表征的校准实验室值之间的直接比较。对于伽马射线，BPD测得的吸收剂量与RCL基准值一致≤3.8%。对于中子，结果表明，BPD不敏感，即，BPD仅检测到来自252Cf的伽马射线剂量成分。从60Co和252Cf获得的伽马射线的LET光谱与这些伽马射线能量的预期一致，但是来自137Cs伽马射线的LET光谱有很大不同。这种差异的潜在原因是137Cs的高剂量率和137Cs伽马射线产生的较低的二次电子能量。然而,这些都不会导致吸收剂量的误差。根据与NIST可追溯标准的比较，显然,BPD可以从低LET带电粒子准确地测量吸收剂量。由于预期的次级中子注量较低，传感器对中子的不敏感性不太可能成为BioSentinel任务的限制。
