Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi’s measurement in a low Earth orbit
Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi’s measurement in a low Earth orbit
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硬X射线望远镜中质子诱发的放射性背景建模：基于Geant4的模拟及其在近地轨道上通过Hitomi测量进行的演示
DOI：
10.1016/j.nima.2018.02.071
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
... (13番目/50人中)
中科院分区：
文献类型：
--
作者：
H. Odaka;M. Asai;K. Hagino;...;K. Hayashi;... (13番目/50人中)
由于宇宙射线质子和/或地磁俘获质子引起的放射性激活，轨道上的硬 X 射线天文台受到大量背景的影响。在完整的蒙特卡罗模拟的框架内，我们提出了以放射性为主的在轨仪器背景的建模。为了减少直接模拟活化同位素延迟发射所需的计算时间，我们插入了半解析计算，将初级质子相互作用产生放射性同位素的概率转换为所有次级同位素测量时的衰变率。因此，我们的模拟方法分为三个步骤：（1）同位素产生的模拟，（2）衰变速率的半解析转换，以及（3）测量时同位素衰变的模拟。该方法通过具有 CdTe 半导体探测器的简单设置进行了验证，并且显示效率比直接模拟提高了 100 倍。为了证明其实验性能，该模拟框架根据瞳X射线天文卫星上的硬X射线成像仪中的CdTe传感器测量的数据进行了测试，该卫星被置于高度为570公里、倾角为31°的近地轨道上，因此在穿过南大西洋异常区时受到了地磁捕获质子的大量辐射。该模拟能够处理质子辐照的完整历史和多个测量窗口。模拟结果与测量数据非常吻合，表明测量的背景可以通过CdTe探测器本身的质子诱导放射性激活和厚Bi 4 Ge 3 O 12 闪烁体屏蔽、宇宙X射线背景泄漏和反照率伽马射线辐射以及探测器系统中自然污染同位素的发射来很好地描述。
Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps:(1) simulation of isotope production,(2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. The simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi 4 Ge 3 O 12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.
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DOI：
10.1016/j.nima.2016.03.038
发表时间：
2016
期刊：
NIMA
影响因子：
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发表时间：
2003
期刊：
IEEE Trans.Nucl.Sci. Vol.50 No.4
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发表时间：
2004
期刊：
The Astrophysical Journal Supplement Series
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