Abstract 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 (3He) 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 3He 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 ± 0.66) × 10−5 cm−2 s−1, and the thermal and fast neutron flux (in the range 1 to 10 MeV) were (1.44 ± 0.15) × 10−5 cm−2 s−1 and (0.71 ± 0.10) × 10−5 cm−2 s−1, respectively.

中文翻译：

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阳阳地下实验室稀有事件搜索实验中子背景测量

摘要 韩国阳阳地下实验室进行了暗物质搜索、无中微子双β衰变等多项实验，由于探测器系统和环境的原因，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。需要确定实验地点的中子通量以设计合适的屏蔽系统和精确的背景估计。我们使用带有 Helium-3 (3He) 正比计数器的 Bonner 球体光谱仪测量了中子谱。地下实验室的中子通量非常低，以致于探测器中包含的放射性同位素的放射性衰变对中子测量产生了显着的背景干扰。使用蒙特卡罗模拟，估计了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 粒子背景后，从 3He 正比计数器的脉冲高度谱中测量每个邦纳球的中子计数率。使用展开技术确定中子通量和能谱。测得的总中子通量为 (4.46 ± 0.66) × 10−5 cm−2 s−1，热和快中子通量（范围 1 至 10 MeV）为 (1.44 ± 0.15) × 10−5 cm−分别为 2 s-1 和 (0.71 ± 0.10) × 10-5 cm-2 s-1。在减去 α 粒子背景后，从 3He 正比计数器的脉冲高度谱中测量每个邦纳球的中子计数率。使用展开技术确定中子通量和能谱。测得的总中子通量为 (4.46 ± 0.66) × 10−5 cm−2 s−1，热和快中子通量（1 至 10 MeV 范围内）为 (1.44 ± 0.15) × 10−5 cm−分别为 2 s-1 和 (0.71 ± 0.10) × 10-5 cm-2 s-1。在减去 α 粒子背景后，从 3He 正比计数器的脉冲高度谱中测量每个邦纳球的中子计数率。使用展开技术确定中子通量和能谱。测得的总中子通量为 (4.46 ± 0.66) × 10−5 cm−2 s−1，热和快中子通量（1 至 10 MeV 范围内）为 (1.44 ± 0.15) × 10−5 cm−分别为 2 s-1 和 (0.71 ± 0.10) × 10-5 cm-2 s-1。