面向辐射环境监测的反康普顿γ能谱仪蒙特卡罗模拟研究
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摘要
使用蒙特卡罗软件Geant4设计模拟了一套用于核事故等辐射环境监测的反康普顿γ能谱仪.主探测器采用HPGe探测器,选择新型闪烁体晶体LaBr3(Ce)作为次级探测器.利用Geant4对探测器系统进行模拟优化,确定最佳的探测器尺寸和结构.模拟的γ射线能量范围从500到1500keV.结果表明,增加主体LaBr3(Ce)晶体厚度能显著提升康普顿抑制系数,当主体LaBr3(Ce)晶体厚度达到60mm时,提升效果明显减弱;在HPGe探测器的后方添加LaBr3(Ce)晶体也能一定程度提升抑制效果,而在HPGe探测器的前方增加LaBr3(Ce)晶体厚度对康普顿抑制系数的提升非常有限.在最优化条件下模拟测量了放射性核素I-131,Cs-134,Cs-137和K-40,对发射单能γ射线的Cs-137和K-40康普顿抑制效果很好,对存在级联衰变的I-131和Cs-134抑制效果相对较弱.
In this study,the Geant4 toolkit is used to simulate a Compton suppression system based upon HPGe primary detector for radioactive environment such as nuclear plant accident.LaBr3(Ce)crystal is selected for the anti-coincidence secondary detector.Simulations for the detector system are performed to gain the optimal sizes for 500~1500 keVγrays.Simulation results show that the Peak Compton Suppression Factors(Peak CSFs)increase significantly with the thickness increase of the body LaBr3(Ce)crystal from 10 to 60 mm,the Peak CSFs do not increase obviously after the thickness of the body LaBr3(Ce)crystal reaches 60-70 mm.Moreover,by adding a LaBr3(Ce)crystal to the back of the HPGe detector can also improve the Peak CSFs,but by adding a LaBr3(Ce)crystal to the front of the HPGe detector has little effect on improving the Peak CSFs.Finally,we simulate a variety of sources in our Compton suppression system under the optimal conditions:for Cs-137 and K-40 that decay via a singleγemission Compton suppression effects are good;for I-131 and Cs-134 that decay in cascade some improvements are still obtained.
In this study,the Geant4 toolkit is used to simulate a Compton suppression system based upon HPGe primary detector for radioactive environment such as nuclear plant accident.LaBr3(Ce)crystal is selected for the anti-coincidence secondary detector.Simulations for the detector system are performed to gain the optimal sizes for 500~1500 keVγrays.Simulation results show that the Peak Compton Suppression Factors(Peak CSFs)increase significantly with the thickness increase of the body LaBr3(Ce)crystal from 10 to 60 mm,the Peak CSFs do not increase obviously after the thickness of the body LaBr3(Ce)crystal reaches 60-70 mm.Moreover,by adding a LaBr3(Ce)crystal to the back of the HPGe detector can also improve the Peak CSFs,but by adding a LaBr3(Ce)crystal to the front of the HPGe detector has little effect on improving the Peak CSFs.Finally,we simulate a variety of sources in our Compton suppression system under the optimal conditions:for Cs-137 and K-40 that decay via a singleγemission Compton suppression effects are good;for I-131 and Cs-134 that decay in cascade some improvements are still obtained.
引文
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[12]Britton R,Burnett J L,Davies A V,et al.MonteCarlo optimisation of a Compton suppression system for use with a broad-energy HPGe detector[J].Nucl Instrum Meth A,2014,762:42.
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[14]Britton R.Compton suppression systems for environmental radiological analysis[J].J Radioanal Nucl Ch,2012,292:33.
[15]Britton R,Burnett J L,Davies A V,et al.Improving the effectiveness of a low-energy Compton suppression system[J].Nucl Instrum Meth A,2013,729:64.
[16]王永昌,王连滨,袁俊谦,等.高纯锗-塑料闪烁体反康普顿γ能谱仪[J].兰州大学学报:自然科学版,1987,23:40.
[2]万恩源,郑向东,万国江,等.2011年春季日本福岛核泄漏污染输送:贵阳131I和137 Cs观测示踪分析[J].环境科学学报,2012,32:2182.
[3]王蕾,郑国栋,赵顺平,等.日本福岛核事故对我国大陆环境影响[J].辐射防护,2012,32:325.
[4]盛黎,周斌,孙明华,等.日本福岛核事故对我国辐射环境影响的监测和分析[J].气象,2013,39:1490.
[5]Morino Y,Ohara T,Nishizawa M.Atmospheric behavior,deposition,and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011[J].Geophys Res Lett,2011,38:L00G11.
[6]Chino M,Nakayama H,Nagai H,et al.Preliminary estimation of release amounts of 131I and 137 Cs accidentally discharged from the Fukushima Daiichi nuclear power plant into the atmosphere[J].J Nucl Sci Technol,2011,48:1129.
[7]Kawamura H,Kobayashi T,Faruno A,et al.Preliminary numerical experiments on oceanic dispersion of 131I and 137 Cs discharged into the ocean because of the Fukushima Daiichi nuclear power plant disaster[J].J Nucl Sci Technol,2011,48:1349.
[8]Bystritsky V M,Zubare E V,Krasnoperov A V,et al.Gamma detectors in explosives and narcotics detection systems[J].Phys Part Nuclei Lett,2013,10:566.
[9]Quarati F G A,Owens A,Dorenbos P,et al.High energy gamma-ray spectroscopy with LaBr3scintillation detectors[J].Nucl Instrum Meth A,2011,629:157.
[10]谢希成,赖万昌,赵祖龙,等.LaBr3(Ce)与NaI(Tl)闪烁探测器的性能研究与比较[J].核电子学与探测技术,2014,34:917.
[11]Allison J,Amako K,Apostolakis J,et al.Recent developments in Geant4[J].Nucl Instrum Meth A,2016,835:186.
[12]Britton R,Burnett J L,Davies A V,et al.MonteCarlo optimisation of a Compton suppression system for use with a broad-energy HPGe detector[J].Nucl Instrum Meth A,2014,762:42.
[13]Britton R,Burnett J L,Davies A V,et al.Determining the efficiency of a broad-energy HPGe detector using Monte Carlo simulations[J].J Radioanal Nucl Ch,2013,295:2035.
[14]Britton R.Compton suppression systems for environmental radiological analysis[J].J Radioanal Nucl Ch,2012,292:33.
[15]Britton R,Burnett J L,Davies A V,et al.Improving the effectiveness of a low-energy Compton suppression system[J].Nucl Instrum Meth A,2013,729:64.
[16]王永昌,王连滨,袁俊谦,等.高纯锗-塑料闪烁体反康普顿γ能谱仪[J].兰州大学学报:自然科学版,1987,23:40.
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