A neutron detector array consisting of a cylindrical plastic scintillator and 24 Helium-3 proportional counters is developed for the detection of neutrons with an extremely low rate. This detector array is designed for the JUNA (Jinping Underground Nuclear Astrophysics laboratory) project to measure the 13C ( α , n) 16O reaction cross-section at stellar energies in CJPL (China Jinping Underground Laboratory). In this paper, we introduce the design of this detector array. The responses of the plastic scintillator to gamma rays and neutrons are tested at the ground level by shielding the detector array with a lead room. The neutron detection efficiency is obtained with a 252Cf source and a PuC source. The measured result is reproduced by Monte Carlo simulation. The coincidence measurement between plastic scintillator and Helium-3 counters is also performed and the coincidence times are obtained. These tests lay the foundation for the future measurement of the 13C ( α , n) 16O reaction cross-section in CJPL.
