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在中子反应截面测量中, 瞬发γ射线法是一种通过测量核反应放出的特征γ射线来得到截面数据的方法, 这种方法能够避免竞争反应道产生的干扰. 但是瞬发γ射线法为在线实验, 本底来源丰富, 造成了在线实验谱分析难度大, 结果不确定性高. 本文研究了使用瞬发γ射线法测量中子诱发伽马产生截面的谱分析技术, 总结了中子诱发伽马产生截面测量中不同特征峰形成的物理过程, 降低了在线实验谱处理过程中计算效应峰净面积的不确定度. 通过采用各种响应函数来对全能峰、本底以及干扰因素进行拟合的方法, 精确提取了效应峰的净面积. 针对弱峰的净面积, 本方法可将峰区域选取引起的波动从30%降低到1%以内, 且净面积拟合值与理论值的差距与统计不确定度相当; 对于解重峰, 本方法所得结果与理论值差距显著低于1%. 通过效率曲线分析、拟合优度计算等方法同时验证了谱分析方法的可靠性.In neutron reaction cross-section measurements, the prompt gamma ray method is a method of obtaining cross-section data by measuring the characteristic gamma rays emitted by a nuclear reaction, thereby avoiding the interference generated by competing reaction channels. However, the prompt gamma ray method is an on-line experiment with abundant background sources, high background counts of the obtained experimental spectra, and numerous interferences such as weak peaks, overlapping peaks, Compton scattering peaks, and neutron effect peaks of Ge in HPGe, which cause the difficulty in analysing the on-line experimental spectra and the high uncertainty in the results. In this work, we study and summarise the spectrum analysis techniques of the prompt gamma ray method that can be used for measuring the neutron cross-section, and comprehensively consider the physical processes of the formation of different characteristic peaks of the prompt gamma ray method, so as to reduce the uncertainty of calculating the net area of the effect peaks in the process of on-line experimental spectrum processing. The Compton edge, weak peaks, overlapping peaks, and the neutron response peaks of the HPGe detector on-line experiment are discussed and analysed, and the net area of the effect peaks is accurately extracted by combining several reasonable functions to fit the total energy peak, the background, and the interferences. For the net area of weak peaks, this method can reduce the peak area selection caused fluctuation from 30% to less than 1%, and the difference between the fitted value of the net area and the theoretical value is comparable to the statistical uncertainty; for the overlapping peaks’ decomposition, the difference between the results obtained by this method and the theoretical value is significantly lower than 1%. The reliability of the spectral analysis method is simultaneously verified by efficiency curve analysis and goodness-of-fit calculation.
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Keywords:
- prompt γ ray method /
- gamma production cross-section /
- spectral analysis /
- neutron /
- hyperpure germanium
[1] 葛智刚, 陈永静 2015 科学通报 60 3087
Ge Z G, Chen Y J 2015 Sci. Bull. 60 3087
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图 1 瞬发γ射线平台在线实验装置示意图
Fig. 1. Schematic diagram of online experimental setup of prompt γ ray platform.
图 2 Clover探测器特征峰参数拟合 (a) δ拟合结果; (b) β拟合结果
Fig. 2. Clover detector characteristic peak parameter fitting: (a) δ fitting results; (b) β fitting results.
图 3 Clover探测器不同源距同一能量的特征γ射线峰峰形对比 (a) 344.278 keV射线峰; (b) 1212.948 keV射线峰
Fig. 3. Comparison of the peak shapes of the characteristic gamma ray peaks of the clover detector at different source distances and the same energy: (a) 344.278 keV ray peak; (b) 1212.948 keV ray peak.
图 4 同轴HPGe特征峰参数拟合 (a) δ拟合结果; (b) β拟合结果
Fig. 4. Parameter fitting of coaxial HPGe of the characteristic gamma ray peaks: (a) δ fitting results; (b) β fitting results.
图 5 同轴HPGe探测器不同源距同一能量的特征γ射线峰峰形对比 (a) 443.965 keV射线峰; (b) 1212.948 keV射线峰
Fig. 5. Comparison of the peak shapes of the characteristic gamma-ray peaks of coaxial HPGe detectors with different source distances at the same energy: (a) 443.965 keV ray peak; (b) 1212.948 keV ray peak.
图 7 152Eu中1085.837 keV与1089.737 keV拟合结果
Fig. 7. Fitting results of 1085.837 keV and 1089.737 keV in 152Eu.
图 8 多源刻度谱中409.462 keV与411.116 keV形成的重峰拟合结果
Fig. 8. Fitting results of overlapping peak formed by 409.462 keV and 411.116 keV in multisource spectrum.
图 9 是否包含康普顿边缘部分本底拟合结果比较, 其中插图为GammaVision处理效果
Fig. 9. Comparison of background fitting results with or without Compton edges, insert is GammaVision processing effect.
图 10 1.2 MeV中子与Fe样品反应的在线实验谱
Fig. 10. Online experimental spectrum of the reaction of 1.2 MeV neutron with Fe sample.
图 11 56Fe(n, n' )发射的846.8 keV射线峰本底扣除效果
Fig. 11. Peak background subtraction effect of 846.8 keV ray emitted by 56Fe(n, n' ).
表 1 锗的多种同位素与中子的主要非弹性散射峰[17]
Table 1. Major inelastic scattering peaks of various isotopes of Ge with neutrons.
反应类型 (n, n'γ) (n, n'e–) 锗的同位素 70Ge 72Ge 74Ge 76Ge 70Ge 72Ge γ 射线能量/keV 176.2 630.0 595.9 545.5 1215.4 691.6 1039.3 834.1 608.4 562.9 — — — — 867.9 1108.4 — — — — 1204.2 — — — 
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表 2 不同ROI区域两种处理方法计数
Table 2. Counts of two method for different ROI regions.
γ射线能量/keV ROI区域/chanel GammaVision 高斯拟合 本工作 656.16 3507—3538 3567 3714 3405 3496—3549 3816 3552 3398 3480—3563 2745 3448 3344 841.574 4505—4527 2588 2709 2780 4484—4547 3047 2947 2882 4468—4563 4460 3054 2947
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表 3 三种方法求取121.781 keV的净面积
Table 3. Net area of 121.781 keV is obtained by three methods.
121.781 keV GammaVision 本文 净面积 1982068 2107410
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[1] 葛智刚, 陈永静 2015 科学通报 60 3087
Ge Z G, Chen Y J 2015 Sci. Bull. 60 3087
[2] 卢希庭 2000 原子核物理(北京: 原子能出版社) 第168页
Lu X T 2000 Nuclear Physics (Beijing: Atomic Energy Press) p168
[3] 石宗仁 2002 原子核物理评论 19 42
Google Scholar
Shi Z R 2002 Nucl. Phys. Rev. 19 42
Google Scholar
[4] EG&G ORTEC 1998 Gamma Vision Software Manual 82
[5] CANBERRA 2002 Gennie2000 Software Manual p113
[6] Hammed M A, Gray P W, Naboulsi A H, Mac Mahon T C 1993 Nucl. Instr. Meth. A 344 543
[7] 孙琪, 王朝辉, 张奇玮, 黄翰雄, 任杰, 阮锡超, 刘世龙, 鲍杰, 栾广源, 丁琰琰, 陈雄军, 聂阳波, 刘超, 赵齐, 王金成, 贺国珠, 杜树斌 2022 原子能科学技术 56 816
Sun Q, Wang Z H, Zhang Q W, Huang H X, Ren J, Ruan X C, Liu S L, Bao J, Luan G Y, Ding Y Y, Chen X J, Nie Y B, Liu C, Zhao Q, Wang J C, He G Z, Du S B 2022 Atomic Energy Science and Technology 56 816
[8] Wu H Y, Li Z H, Tan H, Hua H, Li J, Henning W, Warburton W K, Luo D W, Wang X, Li X Q, Zhang S Q, Xu C, Chen Z Q, Wu C G, Jin Y, Lin J, Jiang D X, Ye Y L 2020 Nucl. Instr. Meth. A 975 164
[9] 吴鸿毅, 李智焕, 吴婧, 华辉, 王翔, 李湘庆, 徐川 2021 科学通报 66 3553
Wu H Y, Li Z H, Wu J, Hua H, Wang X, Li X Q, Xu C 2021 Sci. Bull. 66 3553
[10] Luo D W, Wu H Y, Li Z H, Xu C, Hua H, Li X Q, Wang X, Zhang S Q, Chen Z Q, Wu C G, Jin Y, Lin J 2021 Nucl. Sci. Tech. 32 79
Google Scholar
[11] Phillips G W, Marlow K W 1976 Nucl. Instr. Meth. A 137 525
Google Scholar
[12] Günter Kanisch 2017 Nucl. Instr. Meth. A 855 118
Google Scholar
[13] Helmer R G, Hardy J C, Iacob V E, Sanchez-Vega M, Neilson R G, Nelson J 2003 Nucl. Instr. Meth. A 511 360
Google Scholar
[14] Uher J, Roach G, Tickner J 2010 Nucl. Instr. Meth. A 619 457
Google Scholar
[15] 王思广, 冒亚军, 唐培家, 李泽 2006 核技术 29 495
Google Scholar
Wang S G, Mao Y J, Tang P J, Li Z 2006 Nucl. Sci. Tech. 29 495
Google Scholar
[16] 卢希庭 2000原子核物理 (北京: 原子能出版社) 第65页
Lu X T 2000 Nuclear Physics (Beijing: Atomic Energy Press) p65
[17] Table of Radioactive Isotopes, Chu S Y F, Ekström L P, Firestone R B http://nucleardata.nuclear.lu.se/toi/listnuc.asp?sql=&Z=32 [2023-11-3]
[18] Anđelić B, Knežević D, Jovančević N, Krmar M, Petrović J, Toth A, Medić Ž, Hansman J 2017 Nucl. Instr. Meth. A 852 80
Google Scholar
[19] Gete E, Measday D F, Moftah B A, Saliba M A, Stocki T J 1997 Nucl. Instrum. Methods Phys. A 388 212
Google Scholar
[20] Longoria L C, Naboulsi A H, Gray P W, MacMahon T D 1990 Nucl. Instr. Meth. A 299 308
Google Scholar
[21] Nelson R O, Fotiades N, Devlin M, Becker J A, Garrett P E, Younes W 2005 AIP Conf. Proc. on Nuclear Data For Science and Technology New Mexico, United States, May 24, 2005 p838
[22] Negret A, Borcea C, Dessagne Ph, Kerveno M, Olacel A, Plompen A J M, Stanoiu M 2014 Phys. Rev. C 90 034602
Google Scholar
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