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The combination of a 3He proportional counter and a 4He proportional counter sharing the same parameters was employed as the low background thermal neutron detector. The wall material is oxygen-free copper for low surface a emit rate. Other characters including wall effect and energy resolution were also optimized for low background performance. A portable readout electronics system has been developed and the output of the charge sensitive preamplifier was directly digitized for offline analysis. The risetime from 10% to 60% was selected as the estimation for the electron delay time which proves to be useful in the discrimination of neutron events and backgrounds. The detector system can achieve a thermal neutron sensitivity of 45 cm2 with the background at the level of 0.03 cpd by selecting proper region of interest (ROI). The system was installed in the shield structure of China Dark matter Experiment 1B (CDEX-1B) and reports the thermal neutron flux to be 7.9 × 10−9 ∼ 4.2 × 10−8 cm−2 s−1 at the confidence level of 90%.
Department of Engineering Physics, Tsinghua University and the Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China
Department of Engineering Physics, Tsinghua University and the Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China
Department of Engineering Physics, Tsinghua University and the Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China
Department of Engineering Physics, Tsinghua University and the Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China