Development of a Time-Gated Epithermal Neutron Spectrometer for Resonance Absorption Measurements Driven by a High-Intensity Laser

The advance of laser-driven neutron sources (LDNSs) has enabled neutron resonance spectroscopy to be performed with a single shot of a laser. In this study, we describe a detection system of epithermal (similar to eV) neutrons especially designed for neutron resonance spectroscopy. A time-gated photomultiplier tube (PMT) with a high cut-off ratio was introduced for epithermal neutron detection in a high-power laser experiment at the Institute of Laser Engineering, Osaka University. We successfully reduced the PMT response to the intense hard X-ray generated as a result of the interaction between laser light and the target material. A time-gated circuit was designed to turn off the response of the PMT during the laser pulse and resume recording the signal when neutrons arrive. The time-gated PMT was coupled with a 6Li glass scintillator, serving as a time-of-flight (TOF) detector to measure the neutron resonance absorption values of 182W and 109Ag in a laser-driven epithermal neutron generation experiment. The neutron resonance peaks at 4.15 eV of 182W and 5.19 eV of 109Ag were detected after a single pulse of laser at a distance of 1.07 m.