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arXiv 2102.07205nucl-ex
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YangYang地下实验室中稀有事件搜索实验的中子本底测量

Neutron background measurement for rare event search experiments in the YangYang Underground Laboratory

Young Soo Yoon, Jungho Kim, Hyeonseo Park

摘要:

在大韩民国的YangYang地下实验室进行了一些实验,如寻找暗物质和寻找无中微子双β衰变,由于探测器系统和环境的原因,这些实验需要极低的背景事件率。在地下实验中,中子已被确定为背景源之一。为了设计合适的屏蔽系统和进行精确的本底估算,需要确定实验场的中子通量。我们用Bonner球谱仪和He-3($^{3}$ He)正比计数器测量了中子能谱。地下实验室的中子通量非常低,以至于探测器中放射性同位素的放射性衰变对中子测量产生了显著的背景干扰。使用蒙特卡罗模拟,估计由于探测器材料中的放射性同位素引起的固有$α$背景分布。在减去$α$粒子背景之后,从$^{3}$ He正比计数器的脉冲高度谱测量每个邦纳球的中子计数率。用展开技术测定了中子通量和能谱。测得的总中子通量为(4.46 $\pm$ 0.66)$\times$ $10^{-5}$ $\rm{cm^{-2} s^{-1}}$,热中子通量和快中子通量(1 - 10 MeV)分别为(1.44 $\pm$ 0.15)$\times$ 10 $^{-5}$ $\rm{cm^{-2} s^{-1}}$和(0.71 $\pm$ 0.10)$\times$ 10 $^{-5}$ $\rm{cm^{-2} s^{-1}}$。

英文摘要:

Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double-beta decay, which require an extremely low background event rate due to the detector system and the environment. In underground experiments, neutrons have been identified as one of the background sources. The neutron flux in the experimental site needs to be determined to design a proper shielding system and for precise background estimation. We measured the neutron spectrum with a Bonner sphere spectrometer, with Helium-3 ($^{3}$He) proportional counters. The neutron flux at the underground laboratory was so low that the radioactive decays from the radioisotopes contained in the detector created a significant background interference to the neutron measurement. Using Monte Carlo simulations, the intrinsic $α$ background distribution due to the radioactive isotopes in the detector materials, was estimated. The neutron count rate of each Bonner sphere was measured from the pulse height spectrum of the $^{3}$He proportional counter, after subtracting the $α$ particle background. The neutron flux and the energy spectrum were determined using the unfolding technique. The total neutron flux measured was (4.46 $\pm$ 0.66) $\times$ $10^{-5}$ $\rm{cm^{-2} s^{-1}}$, and the thermal and fast neutron flux (in the range 1 to 10 MeV) were (1.44 $\pm$ 0.15) $\times$ 10$^{-5}$ $\rm{cm^{-2} s^{-1}}$ and (0.71 $\pm$ 0.10) $\times$ 10$^{-5}$ $\rm{cm^{-2} s^{-1}}$, respectively.

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