Environmental sub-MeV neutron measurement at the Gran Sasso surface laboratory with a super-fine-grained nuclear emulsion detector
Environmental sub-MeV neutron measurement at the Gran Sasso surface laboratory with a super-fine-grained nuclear emulsion detector
复制标题
使用超细粒度核乳剂探测器在格兰萨索表面实验室进行环境亚兆伏中子测量
DOI：
10.1103/physrevc.107.014608
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发表时间：
2023
影响因子：
3.1
通讯作者：
Sato O.
中科院分区：
文献类型：
--
作者：
Shiraishi T.;Akamatsu S.;Naka T.;Asada T.;De Lellis G.;Tioukov V.;Rosa G.;Kobayashi R.;D'Ambrosio N.;Alexandrov A.;Sato O.
环境中子的测量在寻找新的物理学（如暗物质粒子）时特别重要，因为中子构成了一个通常不可约的背景源。在亚MeV尺度下测量中子能谱在技术上是困难的，因为它需要非常好的能量分辨率和非常高的射线抑制功率。在这项研究中，我们使用了一种超细颗粒的核乳胶，称为纳米成像跟踪器，作为中子探测器。中子的主要目标是乳胶膜的氢（质子）含量。通过拓扑分析，由中子散射引起的质子反冲可以被检测为亚微米精度的轨道。该方法具有极高的射线抑制能力，其水平相当于环境射线的5年积累，即使在亚MeV能区也具有很好的能量和方向分辨率。为了在充分统计的情况下进行测量，我们升级了自动扫描系统，使其速度达到250 g/（年机器）。我们用880 keV单色中子校准了该系统的探测器性能：发现所有相关运动学变量与预期非常一致。将开发的方法应用于INFN Gran Sasso表面实验室暴露的样品，首次测量了质子能量范围在0.25和1 MeV之间（对应于0.25和10 MeV之间的中子能量范围）的亚MeV环境中子通量，与预测一致。中子能量和方向分布也显示出良好的一致性。
The measurement of environmental neutrons is particularly important in the search for new physics, such as dark matter particles, because neutrons constitute an often irreducible background source. The measurement of the neutron energy spectra in the sub-MeV scale is technically difficult because it requires a very good energy resolution and a very high-ray rejection power. In this study, we used a super-fine-grained nuclear emulsion, called nano imaging tracker, as a neutron detector. The main target of neutrons is the hydrogen (proton) content of emulsion films. Through a topological analysis, proton recoils induced by neutron scattering can be detected as tracks with submicrometric accuracy. This method shows an extremely high-ray rejection power, at the level of, which is equivalent to five years accumulation of environmentalrays, and a very good energy and direction resolution even in the sub-MeV energy region. In order to carry out this measurement with sufficient statistics, we upgraded the automated scanning system to achieve a speed of 250 g/(year machine). We calibrated the detector performance of this system with 880 keV monochromatic neutrons: a very good agreement with the expectation was found for all the relevant kinematic variables. The application of the developed method to a sample exposed at the INFN Gran Sasso surface laboratory provided the first measurement of sub-MeV environmental neutrons with a flux ofin the proton energy range between 0.25 and 1 MeV (corresponds to neutron energy range between 0.25 and 10 MeV), consistent with the prediction. The neutron energy and direction distributions also show a good agreement.