多球中子谱仪的周围剂量当量转换研究
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摘要
以辐射场全能段中子能谱获取及周围剂量当量转换为目的,针对一套以3He正比计数器为探测器的多球中子谱仪,介绍了采用脉冲幅度分析法进行中子-γ甄别,准确测量中子计数率的方法;测量并获取了实验室本底环境中子、Am-Be中子源、氘氘中子管连续出射中子三种辐射场的中子能谱,并予以分析;基于中子能谱进行周围剂量当量转换,分析了不同能量段中子所占的剂量比重,发现快中子是主要贡献者;在比较测量中,对三种单慢化体中子剂量仪器产生的误差进行了理论分析,并给出了依靠多球中子谱仪测准中子周围剂量当量的三点建议。多球中子谱仪可以直接测算周围剂量当量,可以指导其它中子剂量仪器的标校,还可以针对具体能量段进行中子防护设计,精准有效指导外照射剂量防护工作的开展。
[Background] Neutron ambient dose equivalent is closely related to neutron energy. Acquisition of the energy spectrum is necessary to calculate the ambient dose equivalent accurately in the neutron radiation field. [Purpose] This study aims at the ambient dose equivalent calculation by shakedown test of multi sphere neutron spectrometer(MNS). [Methods] First of all, pulse height analysis(PHA) method was used for neutron/γ discrimination to precisely measure neutron count rate. Then the neutron energy spectrum was successfully obtained and carefully analyzed in three neutron radiation fields: laboratory background, Am-Be neutron source and DD tube emergency neutron. Neutron fluence was converted into ambient dose equivalent consulting the conversion coefficient recommended by International Commission on Radiological Protection(ICRP) report No.74, and dose contribution weight from neutron in different energy groups was analyzed. Finally, comparison test was made against three other instruments with mono moderator respectively, errors between MNS and them were analyzed theoretically. [Results] Neutron ambient dose equivalent converted from energy spectrum measured by MNS was consistent with the other three dose instruments. No matter what kind of the neutron radiation field is, fast neutrons are the main contributors to the dose. [Conclusion] PHA and pulse height spectrum monitoring is the critical point for neutron energy spectrum measurement. MNS can be used to measure and calculate neutron ambient dose equivalent directly, guide optimal reference radiation for other neutron dose instruments calibration, and radiation protection design against neutron of special energy groups.
[Background] Neutron ambient dose equivalent is closely related to neutron energy. Acquisition of the energy spectrum is necessary to calculate the ambient dose equivalent accurately in the neutron radiation field. [Purpose] This study aims at the ambient dose equivalent calculation by shakedown test of multi sphere neutron spectrometer(MNS). [Methods] First of all, pulse height analysis(PHA) method was used for neutron/γ discrimination to precisely measure neutron count rate. Then the neutron energy spectrum was successfully obtained and carefully analyzed in three neutron radiation fields: laboratory background, Am-Be neutron source and DD tube emergency neutron. Neutron fluence was converted into ambient dose equivalent consulting the conversion coefficient recommended by International Commission on Radiological Protection(ICRP) report No.74, and dose contribution weight from neutron in different energy groups was analyzed. Finally, comparison test was made against three other instruments with mono moderator respectively, errors between MNS and them were analyzed theoretically. [Results] Neutron ambient dose equivalent converted from energy spectrum measured by MNS was consistent with the other three dose instruments. No matter what kind of the neutron radiation field is, fast neutrons are the main contributors to the dose. [Conclusion] PHA and pulse height spectrum monitoring is the critical point for neutron energy spectrum measurement. MNS can be used to measure and calculate neutron ambient dose equivalent directly, guide optimal reference radiation for other neutron dose instruments calibration, and radiation protection design against neutron of special energy groups.
引文
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6 Jiang X F,Cao J,Jiang C Y,et al.Geant4 simulation of multi-sphere spectrometer response function and the detection of 241Am-Be neutron spectrum[J].Nuclear Science&Techniques,2017,28(12):174.DOI:10.1007/s41365-017-0328-2.
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10刘圣康.中子物理[M].北京:原子能出版社,1986:144-145.LIU Shengkang.Neutron physics[M].Beijing:Atomic Energy Press,1986:144-145.
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12国际放射防护委员会.外照射放射防护中使用的换算系数(ICRP report No.74)[M].北京:中国原子能出版社,1998:274-275.International Commission on Radiological Protection.Conversion coefficients for use in radiological protection against external radiation(ICRP report No.74)[M].Beijing:Atomic Energy Press of China,1998:274-275.
13李建平.粒子加速器辐射剂量测量方法及应用[J].辐射防护,2008,28(6):338-342.LI Jianping.Radiation dose measurement methods for particle accelerator[J].Radiation Protection,2008,28(6):338-342.
2 Bramblett R L,Ewing R I,Bonner T W.A new type of neutron spectrometer[J].Nuclear Instruments and Methods,1960,9(1):1-12.
3胡庆东,曾志,马豪,等.室内环境中子能谱及剂量率的多球谱仪测量[J].清华大学学报(自然科学版),2015,55(12):1332-1334.HU Qingdong,ZENG Zhi,MA Hao,et al.Measurement of indoor natural neutron spectrum with a bonner sphere spectrometer[J].Tsinghua University(Science&Technology),2015,55(12):1332-1334.
4李岩,程凡杰,成昱廷,等.利用BF3多柱谱仪测量临界装置中子能谱[J].原子能科学技术,2017,51(2):319-322.LI Yan,CHENG Fanjie,CHENG Yuting,et al.Neutron spectrum measuring of critical assembly by BF3multi-column spectrometer[J].Atomic Energy Science and Technology,2017,51(2):319-322.
5付鑫.宽能谱多球中子谱仪的研制[D].北京:中国科学院大学,2016.FU Xin.Research and development of an extended range multi-sphere neutron spectrometer[D].Beijing:University of Chinese Academy of Sciences,2016.
6 Jiang X F,Cao J,Jiang C Y,et al.Geant4 simulation of multi-sphere spectrometer response function and the detection of 241Am-Be neutron spectrum[J].Nuclear Science&Techniques,2017,28(12):174.DOI:10.1007/s41365-017-0328-2.
7汲长松.中子探测[M].北京:中国原子能出版社,2014:332-334.JI Changsong.Neutron detection[M].Beijing:Atomic Energy Press of China,2014:332-334.
8 FST Sensortechnik.Manual of neutron spectrometer REM500[EB/OL].http://www.fst-sensortechnik.com./seiten/frms1.html.2015.
9陈永浩.反冲质子法快中子能谱测量及解谱技术研究[D].兰州:兰州大学,2013.CHEN Yonghao.Fast neutron energy spectrum measuring and unfolding research by proton recoils method[D].Lanzhou:Lanzhou University,2013.
10刘圣康.中子物理[M].北京:原子能出版社,1986:144-145.LIU Shengkang.Neutron physics[M].Beijing:Atomic Energy Press,1986:144-145.
11 GB/T 14055.1-2008:中子参考辐射第1部分:辐射特性和产生方法[S].北京:中国标准出版社,2008.GB/T 14055.1-2008:Reference neutron radiations-Part 1:characteristics and methods of production[S].Beijing:National Standard Press of China,2008.
12国际放射防护委员会.外照射放射防护中使用的换算系数(ICRP report No.74)[M].北京:中国原子能出版社,1998:274-275.International Commission on Radiological Protection.Conversion coefficients for use in radiological protection against external radiation(ICRP report No.74)[M].Beijing:Atomic Energy Press of China,1998:274-275.
13李建平.粒子加速器辐射剂量测量方法及应用[J].辐射防护,2008,28(6):338-342.LI Jianping.Radiation dose measurement methods for particle accelerator[J].Radiation Protection,2008,28(6):338-342.