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张奇玮, 栾广源, 贺国珠, 程品晶, 阮锡超, 朱兴华. Gamma全吸收型BaF2探测装置中子屏蔽体与吸收体的研究[J]. 原子核物理评论, 2020, 37(3): 771-776. DOI: 10.11804/NuclPhysRev.37.2019CNPC30
引用本文: 张奇玮, 栾广源, 贺国珠, 程品晶, 阮锡超, 朱兴华. Gamma全吸收型BaF2探测装置中子屏蔽体与吸收体的研究[J]. 原子核物理评论, 2020, 37(3): 771-776. DOI: 10.11804/NuclPhysRev.37.2019CNPC30
Qiwei ZHANG, Guangyuan LUAN, Guozhu HE, Pinjin CHEN, Xichao RUAN, Xinghua ZHU. Study of Neutron Shield and Absorber for Gamma Total Absorption Facility[J]. Nuclear Physics Review, 2020, 37(3): 771-776. DOI: 10.11804/NuclPhysRev.37.2019CNPC30
Citation: Qiwei ZHANG, Guangyuan LUAN, Guozhu HE, Pinjin CHEN, Xichao RUAN, Xinghua ZHU. Study of Neutron Shield and Absorber for Gamma Total Absorption Facility[J]. Nuclear Physics Review, 2020, 37(3): 771-776. DOI: 10.11804/NuclPhysRev.37.2019CNPC30

Gamma全吸收型BaF2探测装置中子屏蔽体与吸收体的研究

Study of Neutron Shield and Absorber for Gamma Total Absorption Facility

  • 摘要: 中国原子能科学研究院已经建造完成了我国第一套全吸收型BaF2探测装置,采用瞬发γ测量法,精确测量中子俘获反应截面。中子源是利用HI-13串列加速器产生的脉冲化质子束,通过7Li(p, n)7Be反应建立。为了有效降低周围环境材料和探测器产生的散射中子本底,约束中子束流的形状,使用MCNP程序模拟设计了屏蔽体,采用含硼聚乙烯(B4C质量分数为5%)包裹5 cm铅的方案,以及准直器采用平行孔的方案。该设计使样品处的中子束斑平整均匀,直径约为2 cm,束斑外的中子注量降低5个数量级,γ注量降低3个数量级。同时设计了中子吸收体(外半径为10 cm,厚度为7 cm)用于吸收待测样品产生的散射中子。MCNP和GEANT4程序的模拟结果表明:选择含硼聚乙烯(10B4C质量分数为10%)作为中子吸收体的加工材料,其中子吸收率达到了80%,并设置1 MeV的能量加和阈,能够满足在线测量中子俘获反应截面的实验要求。

     

    Abstract: The first gamma total absorption facility (GTAF) in China has been constructed in China Institute of Atomic Energy, which will be used to accurately measure the neutron capture cross section by prompt gamma method. A neutron source is established by 7Li(p, n)7Be reaction using pulsed proton beams generated by HI-13 tandem accelerator of CIAE. In order to effectively reduce the scattering neutron background produced by surrounding materials and detectors, and restrain the shape of neutron beam, neutron shield with boron-containing polyethylene (5% of B4C) coated with 5 cm lead and collimator of parallel hole are designed by MCNP program. The design makes spot of neutron beam flat and uniform, the diameter is about 2 cm, the flux of neutron outside the beam spot is reduced by 5 orders of magnitude, and the flux of gamma is reduced by 3 orders of magnitude. At the same time, neutron absorber (the outer radius is 10 cm, the thickness is 7 cm) is designed, which is used to absorb the scattered neutrons produced by the sample to be measured. The simulation results of MCNP and GEANT4 show that the boron containing polyethylene (10B4C mass fraction is 10%) is selected as the processing material of neutron absorber, in which the rate of neutron absorption reaches 80%, and the threshold of sum energy is set to 1 MeV, which meets the requirement of on-line experiment about the measurement of neutron capture cross section.

     

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