Measurement of environmental level X, γ dose with conversion of complete spectra without deconvolution method of MC simulation
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摘要: 为了更好地进行环境X/γ辐射剂量的测量，通过对电制冷高纯锗探测器蒙特卡罗建模获取0.01～1.5 MeV能量范围内的能谱和剂量（率）值，并利用无卷积全谱转换法进行能谱-剂量转换研究。研究发现，通过无卷积全谱转换法计算得到的剂量率与模拟剂量率符合较好；通过在中国计量研究院环境γ辐射空气吸收剂量标准辐射场中进行Co-60和Cs-137放射源剂量率实验验证，结果显示，在0.01～1.5 MeV的能量范围内，通过能谱-剂量转换得到剂量率与标准剂量率的误差小于±10%，这表明通过无卷积全谱转换法进行能谱-剂量（率）转换系数的求解是可行的。Abstract: For the accurate measurement of environmental X/γ radiation dose rate, the conversion from energy spectrum to dose rate is used. In this paper, the energy spectrum and dose value of the electrically cooled high-purity germanium detector (HPGe detector) in the energy range of 0.01−1.5 MeV are obtained by Monte Carlo simulation. And the method “Conversion of complete spectra without deconvolution” is used for energy spectrum-dose conversion study. It is found that the dose rate calculated by Conversion of complete spectra without deconvolution method is in good agreement with the simulated dose rate. Experimental verification was carried out in the standard radiation field (Co-60, Cs-137) of the environmental γ radiation air absorbed dose of the China Institute of Metrology, the result shows that in the energy range of 0.01−1.5 MeV, the error between the dose rate value obtained by energy spectrum-dose conversion and the standard dose rate value is less than ±10%. The study shows that it is feasible to solve the energy spectrum-dose (rate) conversion coefficient by the method “Conversion of complete spectra without deconvolution”.
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图 3 高纯锗探测器刻度实验图
Figure 3. Diagram of calibration measuring situation for HPGe detector
图 4 实验探测效率与模拟探测效率对比图
Figure 4. Comparison of experimental detection efficiency and simulated detection efficiency
图 5 高纯锗探测器测量放射源实验装置图
Figure 5. Experimental device for measuring radioactive source with high purity germanium detector
图 6 10L球电离室测量放射源实验装置图
Figure 6. Experimental device for measuring radioactive sources in a 10L spherical ionization chamber
图 8 MCNP模拟Co-60，Cs-137的能谱结果
Figure 8. Energy spectrum of Co-60 and Cs-137 simulated by MCNP
图 11 高纯锗探测器 Co-60能谱
Figure 11. Energy spectrum of Co-60 of high purity germanium detector
图 12 高纯锗探测器 Cs-137的能谱
Figure 12. Energy spectrum of Cs-137 of high purity germanium detector
表 1 高纯锗探测器能量刻度测量结果
Table 1. Result of the calibration measurement of HPGe detector
radioactive source energy/keV FWHM/MeV detection efficiency/% Co-57 122.06 2.74×10−3 0.239 136.47 2.67×10−3 0.274 Co-60 1173.24 3.44×10−3 0.057 1332.51 3.51×10−3 0.052 Cs-137 661.66 3.36×10−3 0.092 Na-22 1274.54 3.17×10−3 0.054 
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表 2 不同死层厚度高纯锗探测器模拟探测效率结果
Table 2. Simulated detection efficiency results of HPGe detector with different dead layer thickness
E/keV experimental
detection
efficiency/%simulated detection efficiency at different dead layer/% 0.05 cm 0.07 cm 0.10 cm 0.12 cm 0.17 cm 0.22 cm 122.06 0.278 0.230 0.273 0.264 0.250 0.228 0.208 136.47 0.275 0.293 0.283 0.288 0.264 0.245 0.227 511.00 0.128 0.078 0.119 0.116 0.116 0.112 0.108 661.66 0.092 0.098 0.098 0.091 0.095 0.092 0.089 1173.24 0.058 0.031 0.063 0.062 0.062 0.060 0.059 1274.54 0.055 0.021 0.060 0.058 0.058 0.056 0.055 1332.51 0.052 0.029 0.057 0.056 0.056 0.054 0.053
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表 3 能量组2号无卷积全谱转换法与模拟剂量率的比较
Table 3. Dose rate of conversion of complete spectra without deconvolution method and simulation of energy group No. 2
average energy/MeV simulated dose
rate/(nGy·h−1)dose rate of conversion of complete spectra
without deconvolution method /(nGy·h−1)residue/
(nGy·h−1)0.055 1.80×10−5 1.80×10−5 0 0.070 1.72×10−5 1.72×10−5 0 1.000 2.20×10−5 2.20×10−5 0 0.125 2.82×10−5 2.82×10−5 9.83×10−20 0.170 4.11×10−5 4.11×10−5 9.49×10−20 0.662 2.00×10−3 2.00×10−3 0 1.250 3.44×10−3 3.44×10−3 9.97×10−18
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表 4 10 L球电离室在不同距离处测量放射源Co-60和Cs-137剂量率结果
Table 4. The results of measuring the dose rate of Co-60 and Cs-137 in a 10 L spherical ionization chamber at different distances
radioactive
sourcedistance/m measured dose
rate/(nGy·h−1)standard value of
dose rate/(nGy·h−1)relative error of measured
value and standard value/%Cs-137 3.0 5343 5397 −1.001 Cs-137 3.5 3965 3962 0.076 Cs-137 4.0 3018 3028 −0.330 Cs-137 4.5 2395.5 2396 −0.021 Co-60 3.0 1368 1355.4 −0.921 Co-60 3.5 1005 988.5 −1.642 Co-60 4.0 769 776.1 0.923 Co-60 4.5 607 602.55 −0.733
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表 5 能量组2号无卷积全谱转换法剂量率值与标准值比较
Table 5. Comparison of dose rate of Conversion of complete spectra without deconvolution method and the standard value
radioactive
sourcedistance/m dose rate of conversion of complete spectra
without deconvolution method/(nGy·h−1)live time
rate/%standard value of
dose rate/(nGy·h−1)relative error of calculated
value and standard value/%Cs-137 3.0 6115.9 0.55 5830.0 8.02 Cs-137 3.5 4497.1 0.63 4286.5 8.19 Cs-137 4.0 3372.5 0.72 3214.1 6.15 Cs-137 4.5 2688.6 0.75 2562.1 6.93 Co-60 3.0 1363.1 0.92 1339.7 −2.07 Co-60 3.5 1010.5 0.93 993.0 −1.20 Co-60 4.0 770.5 0.95 757.0 −1.56 Co-60 4.5 609.7 0.96 598.9 −1.33
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