基于蒙特卡罗方法的点源、体源全能峰效率计算方法研究

摘要/Abstract

摘要： 基于高纯锗探测器效率的积分表达式,通过理论计算全能峰线减弱系数,并结合γ光子在探测器内的不同路径长度,采用蒙特卡罗方法替代数值积分得到全能峰效率期望值。首先模拟验证了N型和P型两种高纯锗谱仪在点源距离探测器5 cm轴向位置处的全能峰效率,模拟结果和实验结果的偏差在±5.24%以内,证明了方法对点源全能峰效率计算的准确性;在点源基础上,通过效率传递方法对体源进行全能峰效率计算,通过树脂、二氧化硅、咖啡灰及气溶胶滤膜4种不同介质的标准源对本方法进行验证,除P型探测器低能端偏差较大外,其余能量的探测效率计算偏差均小于±6.67%。与全过程蒙特卡罗模拟方法相比,本方法不需要专业的建模程序和昂贵的商业软件,仅通过简单编程就可计算点源和体源的高纯锗探测器全能峰效率,对应急条件下的放射性定量分析有较大实际意义。

关键词: 高纯锗探测器, 蒙特卡罗, 全能峰效率, γ谱仪

Abstract: Based on the integral expression of the efficiency of the high purity germanium detector, the full-energy peak linear attenuation coefficients are calculated theoretically. Combined with the different tracks of gamma photons in the detector, the Monte Carlo method is used instead of the numerical integration to obtain the expected value of the full-energy peak efficiency. Firstly, the full-energy peak efficiencies of N-type and P-type high purity germanium spectrometers at the axial position of 5 cm from the point source to the detector are simulated and verified. The deviations between the simulation results and the experimental results are within ± 5.24%, which prove the accuracy of the method for calculating the full-energy peak efficiency of point source. On the basis of the point source efficiency simulation, the full-energy peak efficiency of volume source is simulated by the efficiency transfer method. The method is verified by the standard sources of four different media, namely resin, silica, coffee ash and aerosol filter in the laboratory. Except for the relative large deviations at low energy regions of the P-type detector, the calculation deviations of the other energy detection efficiencies are less than ±6.67%. Compared with the whole-process Monte Carlo simulation method, this method does not require professional modeling programs and expensive commercial software, and can calculate the full-energy peak efficiencies of point sources and volume sources through simple programming, which has great practical significance for quantitative analysis of radioactivity under emergency conditions.

Key words: high-purity germanium detector, Monte Carlo, full-energy peak efficiency, γ spectrometer

中图分类号:

TL817.2

张磊. 基于蒙特卡罗方法的点源、体源全能峰效率计算方法研究[J]. 辐射防护, 2024, 44(5): 445-453.

ZHANG Lei. Research on the calculation method of full-energy peak efficiency of point source and volume source by hybrid Monte Carlo method[J]. RADIATION PROTECTION, 2024, 44(5): 445-453.

参考文献

[1] 李君利. 实验室γ能谱测量与分析[M]. 北京: 人民交通出版社, 2014.
[2] 张磊, 罗丽娟, 李晓凤. MC法模拟宽能型HPGe γ谱仪全能峰效率[J]. 核电子学与探测技术, 2021, 41(5): 800-803.
ZHANG Lei, LUO Lijuan, LI Xiaofeng. Simulation of full-energy peak efficiency of bulk samples for a broad-energy HPGe detector by Monte Carlo method[J]. Nuclear Electronics & Detection Technology, 2021, 41(5): 800-803.
[3] Kaya S, Çeliik N, Bayram T. Effect of front, lateral and back dead layer thicknesses of a HPGe detector on full energy peak efficiency[J]. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2022, 1029: 166401.
[4] Ordóñez J, Gallardo S, Ortiz J, et al. Intercomparison of full energy peak efficiency curves for an HPGe detector using MCNP6 and GEANT4[J]. Radiation Physics and Chemistry, 2019, 155: 248-251.
[5] Moens L, De Donder J, Lin X L, et al. Calculation of the absolute peak efficiency of gamma-ray detectors for different counting geometries[J]. Nuclear Instruments and Methods in Physics Research, 1981, 187(2/3): 451-472.
[6] Piton F, Lépy M C, Be M M, et al. Efficiency transfer and coincidence summing corrections for γ-ray spectrometry[J]. Applied Radiation and Isotopes, 2000, 52(3): 791-795.
[7] Radu D, Stanga D, Sima O. Etna software used for efficiency transfer from a point source to other geometries[J]. Applied Radiation and Isotopes, 2009, 67(9): 1686-1690.
[8] Vidmar T. EFFTRAN-A Monte Carlo efficiency transfer code for gamma-ray spectrometry[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005, 550(3): 603-608.
[9] Abbas M I. HPGe detector photopeak efficiency calculation including self-absorption and coincidence corrections for Marinelli beaker sources using compact analytical expressions[J]. Applied Radiation and Isotopes, 2001, 54(5): 761-768.
[10] Selim Y S, Abbas M I, Fawzy M A. Analytical calculation of the efficiencies of gamma scintillators. Part I: total efficiency for coaxial disk sources[J]. Radiation Physics and Chemistry, 1998, 53(6): 589-592.
[11] Barrera M, Suarez-llorens A, Casas-ruiz M, et al. Theoretical determination of gamma spectrometry systems efficiency based on probability functions. Application to self-attenuation correction factors[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017, 854: 31-39.
[12] Haase G, Tait D, Wiechen A. Monte Carlo simulation of several gamma-emitting source and detector arrangements for determining corrections of self-attenuation and coincidence summation in gamma-spectrometry[J]. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1993, 329(3): 483-492.
[13] 丁富荣, 班勇, 夏宗璜. 辐射物理[M]. 北京: 北京大学出版社, 2004.
[14] Selim Y S,Hussien M S,Fawzy M A, et al. Direct statistical mathematical model to calculate the full energy peakefficiency of HPGe detector sizes[C]//2nd International Workshop on Real-Time Measurement, Instrumentation and Control. Oshawa: IEEE NPSS, 2011: 210.
[15] Berger M J, Hubbell J H, Seltzer S M, et al. XCOM: photon cross sections database, NIST standard reference database 8 (XGAM)[EB/OL]. [网络访问日期缺失]. https://www.nist.gov/pml/xcom-photon-cross-sections-database.
[16] Vidmar T, Likar A. On the invariability of the total-to-peak ratio in gamma-ray spectrometry[J]. Applied Radiation and Isotopes, 2004, 60(2/4): 191-195.
[17] 樊元庆, 王军, 王世联. HPGe γ谱仪峰总比不变性的实验研究[J]. 原子能科学技术, 2006, 40(z1): 122-125.
FAN Yuanqing, WANG Jun, WANG Shilian. Experiment research on invariability of peak-to-total ratio in γ-ray spectrometry[J]. Atomic Energy Science and Technology, 2006, 40(z1): 122-125.
[18] 张磊. γ能谱固体样品的自吸收修正研究[J]. 核技术, 2021, 44(9): 45-50.
ZHANG Lei. Study on self-absorption corrections of γ spectrum for volume samples[J]. Nuclear Techniques, 2021, 44(9): 45-50.
[19] Agarwal C, Poi S, Goswami A, et al. A simple numerical method for gamma-ray self-attenuation correction for samples of common geometries[J]. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008, 597(2/3): 198-202.
[20] Vargas M J, Díaz N C, Sánchez D P. Efficiency transfer in the calibration of a coaxial p-type HpGe detector using the Monte Carlo method[J]. Applied Radiation and Isotopes, 2003, 58(6): 707-712.