Investigation of fast neutron resonance transmission analysis based on the ultrashort pulsed electron beam-driven photoneutron source

摘要

Fast neutron resonance transmission analysis (FNRTA) is an effective method to identify the light nucleus by measuring its characteristic nuclear structure. One of the significant means of performing high-resolution FNRTA is associating a pulsed electron beam-driven photoneutron source with a neutron time of flight (TOF) detection system. The typical beam width which ranges from a few nanoseconds to several microseconds stretches the flight path to tens and even hundreds of meters for the energy resolution requirement and limits the FNRTA to laboratory analysis only. Currently, we can obtain an ultrashort-pulsed electron beam with a width of 8 ps owing to the femtosecond laser techniques. This benefits the energy resolution and accordingly shortens the flight path to a few meters, and dramatically reduces the volume of FNRTA and even makes it moveable. The work reported in this paper configured FNRTA by using an 8-ps-pulsed 45MeV electron beam-driven photoneutron source and a 5-m TOF. Monte Carlo simulations are utilized to provide a detailed evaluation of the source and the energy resolution of TOF. The results illustrate that a pulsed neutron beam with energies ranging from sub keV to more than 10 MeV and with an intensity of 1.925 × 10~8 n/s could be delivered. The energy resolution is evaluated to less than 1.67% within the energy region of 1-10 MeV. Preliminary resonance experiments of graphite are implemented by placing a graphite block close to the target. The resonance structure can be distinguished from the experimental results.