Exploratory run for fast neutron background in an underground laboratory

Fast neutron background above an energy of ~3 MeV in the Jaduguda Underground Science Laboratory (JUSL) was planned to be measured with a 5 inches x 5 inches BC501A liquid scintillator detector. The neutron events resulting in proton recoil were distinguished from the gamma events using Pulse Shape discrimination (PSD). A ²⁴¹Am-Be source was used to determine the required PSD parameter. Data were acquired uninterruptedly for a period of 76 days in the underground laboratory. The pulse height distribution obtained for the recoil protons from neutron-proton scattering is unfolded to determine the energy spectrum of the background neutrons. Energy calibration of the detection system was carried out using the Compton edges of the corresponding photopeaks for ⁶⁰Co and ¹³⁷Cs gamma sources. (author)