Commissioning of the fast neutron detector array at CIAE

An array composed of 48 liquid scintillation detectors and a parallel plate avalanche counter (PPAC) was developed in China Institute of Atomic Energy (CIAE) to measure the PFNS of the actinide nuclei. The efficiency and energy calibration were carried out for all the liquid scintillators, and their efficiency consistency was tested to be better than 5\%.

The time resolution of the PPAC and the liquid scintillator was measured to be 1.08 ns and 1.16 ns with $^{252}$Cf and $^{207}$Bi source, respectively. The pulse shape discrimination (PSD) of the liquid scintillator was utilized to identify neutron and $\gamma$ signals on an event-by-event basis, and the figure of merit (FOM) was deduced as 1.12 at 200 keVee threshold. The contribution to the PFNS from multiple scattered neutron was evaluated by Geant4 simulation and those originate from the environment were found comparative to the crosstalk between detectors. The neutron efficiency of the entire detection array was calibrated by measurement of $^{252}$Cf spontaneous fission source and was demonstrated to be consistent with the Geant4 simulation results, which verified the reliability of the detection array.