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瞬发裂变中子谱（prompt fission neutron spectrum，PFNS）是用于核实验诊断过程中十分重要的参数数据，传统的测量主锕系核素（U，Pu）PFNS的技术手段是采用裂变室，利用裂变碎片标识裂变中子，通过中子飞行时间技术获得裂变中子谱.目前出现了一种新的用于PFNS测量的技术，其原理是基于如下的物理事实：在一次裂变过程中，释放中子的同时伴随着释放7–8个γ射线光子，而非弹性散射效应产生的γ射线光子只有1–2个.据此，可以通过裂变γ射线的多重性将裂变中子和其他杂散中子甄选出来，达到测量PFNS的目的.本文建立了基于裂变γ标识技术的PFNS测量实验系统.利用该系统对252Cf中子源的PFNS进行了实验测量，测量结果与传统的裂变碎片标识法及ENDF/B-VⅡ数据库的标准谱进行了比较，对新方法的裂变标识率以及实验不确定度也一并进行了分析.The high-accuracy nuclear datum of prompt fission neutron spectrum (PFNS) is not only an important parameter for evaluating nuclear data, but also relevant to a more fundamental understanding of the fission process. However, the PFNS experimental data of main actinides (uranium and plutonium) are very scarce and the existing experimental data are in significant discrepancy. The error of some experimental data is markedly large:the relative uncertainty value reaches above 30%. In order to clarify these discrepancies and reduce the uncertainty, more reliable and accurate fission spectrum measurements are necessary. Most of the traditional measurements of the PFNS rely on time-of-flight technique. In this technique the fission sample needs to be prepared in a fission chamber and the fission neutron is identified by fission fragment. Since the particle range of fission fragment is very short, the thickness of sample is limited. So the number of samples cannot be large and the statistic count of fission neutrons will not be great either. Now a new technique to measure PFNS has appeared based on fission gamma multiplicity, which could be used to discriminate fission neutron from other neutrons. The new technique is based on a physical fact:when a fission event happens, seven-to-eight associated gamma photons are emitted while the inelastic scattering effect emits only one or two associated gamma photons. Accordingly, the fission neutron could be discriminated from other neutrons by fission gamma multiplicity. The principles of the new method and the realizing approach are presented in detail. The experimentally measuring system is established. A spontaneous fission neutron source 252Cf is used to measure the PFNS in order to validate the measuring system. The measured spectra are compared with those of ENDF/B-VⅡ library. The PFNS of 238U induced by D-T neutron is measured by the measuring system. The results show that the new method based on fission gamma identification is be available in the measuring of PFNS. The identification efficiency, the total uncertainty analysis of the new method and the suggestion for improvements in the future are also included in the paper.
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Keywords:
- prompt fission neutron spectra /
- fission γ /
- 252Cf spontaneous fission /
- fission γ tagging
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[20] Qin J G 2016 Ph. D. Dissertation (Hefei: University of Science and Technology of China) (in Chinese)[秦建国 2016 博士学位论文 (合肥: 中国科学技术大学)]
[21] Chen J X, Shi Z M, Tang G Y 1993 Nuclear Electronics and Detection Technology 13 323 (in Chinese)[陈金象, 施兆民, 唐国有 1993 核电子学与探测技术 13 323]
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[1] Huang H X, Ruan X C, Ren J, Nie Y B, Li G W, Luan G Y 2017 Nucl. Phys. Rev. 34 252 (in Chinese)[黄翰雄, 阮锡超, 任杰, 聂阳波, 黎光武, 栾广源 2017 原子核物理评论 34 252]
[2] Wen W P, Li G W, Wang H K 2017 At. Eng. Sci. Tech. 51 230 (in Chinese)[文卫平, 黎光武, 王宏凯 2017 原子能科学技术 51 230]
[3] Haight R C, Wu C Y, Lee H Y, Taddeucci T N, Perdue B A, O'Donnell J M, Fotiades N, Devlin M, Ullmann J L, Bredeweg T A, Jandel M, Nelson R O, Wender S A, Neudecker D, Rising M E, Mosby S, Sjue S, White M C, Bucher B, Henderson R 2015 Nucl. Data Sheets 123 130
[4] Haight R C, Lee H Y, Taddeucci T N, O'Donnell J M, Perdue B A, Fotiades N, Devlin M, Ullmann J L, Laptev A, Bredeweg T, Jandel M, Nelson R O, Wender S A, White M C, Wu C Y, Kwan E, Chyzh A, Henderson R, Gostic J 2014 Nucl. Data Sheets 119 205
[5] Neudecker D, Taddeucci T N, Haight R C, Lee H Y, White M C, Rising M E 2016 Nucl. Data Sheets 131 289
[6] Blain E, Daskalakis A, Danon Y 2014 Nucl. Data Sheets 119 209
[7] Kocak M, Ahmadov H, Dere G 2014 Ann. Nucl. Energy 70 82
[8] Noda S, Haight R C, Nelson R O, Devlin M, O'Donnell J M, Chatillon A, Granier T, Bélier G, Taieb J, Kawano T, Talou P 2011 Phys. Rev. C 83 034604
[9] Chatillon A, Bélier G, Granier T, Laurent B, Taïeb J, Noda S, Haight R C, Devlin M, Nelson R O, O'Donnell J M 2014 Phys. Rev. C 89 014611
[10] Ethvignot T, Devlin M, Drosg R, Granier T, Haight R C, Morillon B, Nelson R O, O'Donnell J M, Rochman D 2003 Phys. Lett. 575 221
[11] Taieb J, Laurent B, Bélier G, A Sardet, C Varignon 2016 Nucl. Instrum. Methods Phys. Res. Sect. A 833 1
[12] Blain E, Daskalakis A, Block R C, Barry D, Danon Y 2016 Nucl. Instrum. Methods Phys. Res. Sect. A 805 95
[13] Woodring M L, Egan J E, Kegel G R, Desimone D J 2008 J. Radioanal. Nucl. Che. 276 707
[14] An L, He T, Zheng P, Wang X H, Guo H P, Yang J, Zhu C X, Mou Y F 2013 High Power Laser Particle Beams 25 3045 (in Chinese)[安力, 何铁, 郑普, 王新华, 郭海萍, 阳剑, 朱传新, 牟云峰 2013 强激光与粒子束 25 3045]
[15] He T, Zheng P, Xiao J, Zhu C X, Yang J, Guo H P 2017 Appl. Radiat. Isot. 124 56
[16] Ji C S 1990 Nuclear Detection and Experimental Manual (Beijing: Atom Energy Press) p312 (in Chinese)[汲长松 1990 核辐射探测器及其实验技术手册 (北京: 原子能出版社) 第312页]
[17] Yan J, Li C, Liu R, Jiang L, Lu X X, Wang M 2011 Acta Phys. Sin. 60 32901 (in Chinese)[言杰, 李澄, 刘荣, 蒋励, 鹿心鑫, 王玫 2011 物理学报 60 32901]
[18] Li J S, Zhang Y, Jin Y, Li R L 2001 Nuclear Electronics and Detection Technology 21 264 (in Chinese)[李建胜, 张翼, 金宇, 李润良 2001 核电子学与探测技术 21 264]
[19] Hansena W, Richter D 2002 Nucl. Instrum. Methods Phys. Res. Sect. A 476 195
[20] Qin J G 2016 Ph. D. Dissertation (Hefei: University of Science and Technology of China) (in Chinese)[秦建国 2016 博士学位论文 (合肥: 中国科学技术大学)]
[21] Chen J X, Shi Z M, Tang G Y 1993 Nuclear Electronics and Detection Technology 13 323 (in Chinese)[陈金象, 施兆民, 唐国有 1993 核电子学与探测技术 13 323]
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