Measurement of relative neutron energy response curve of plastic scintillator detector based on the back-n-white neutron source at CSNS

The plastic scintillator detector is widely used to measure pulsed radiation fields, and a high-quality neutron energy response curve is crucial for accurately determining neutron yields. Traditionally, the neutron energy response curve can be obtained by the simulation of the performance of neutron detectors via the knowledge of the light yield of secondary particles or direct measuring energy response. Both methods record signals by a data acquisition system in the counting mode. This work establishes a new model to directly measure the energy response to neutrons of a plastic scintillator detector in current mode with white source spectra. The plastic scintillator detector can be triggered externally. There is no signal loss and dead time, and it is possible to calibrate the neutron detector with a high-intensity neutron source. Efficiencies can be determined at all energies simultaneously, and a rapid calibration of the plastic scintillator detector is available. To validate the experimental results, the theoretical values are obtained by Geant4 simulation, and the results reproduce the shapes of the experimental curves reasonably well. The neutron energy response curves of the detector show that when the thickness of the scintillator is reduced from 3 to 1 mm, the reduction ratio of gamma signal intensity is greater than that of neutron signal intensity, which leads to an increase in the neutron-gamma sensitivity ratio. Meanwhile, the thin scintillator thickness can obtain a somewhat flatter neutron energy response curve compared with other thicknesses.