Investigation of the light output properties of organic scintillators in a neutron-scatter TOF spectrometer for improved fast neutron spectroscopy

The neutron-scatter time-of-flight (TOF) spectrometer, utilizing two organic scintillation detectors, enables the characterization of fast neutron spectra with a more compact setup compared to conventional TOF methods. To estimate the incident neutron energy $E_{n0}=E_p$ + $E_{n^{\prime }}$, the energy $E_p$ of the recoil proton produced from neutron scattering on hydrogen is obtained by inverting the measured light intensity from the first detector. Meanwhile, the energy $E_{n^{\prime }}$ of the scattered neutron is determined using the TOF measurement between the two detectors. However, our simulations indicate that light output associated with neutron scatterings on carbon and/or sequential multiple scatterings can cause deviations when retrieving the recoil proton energy $E_p$, leading to underestimations of the energies for some measured neutrons and distortion of the neutron spectrum, particularly in the low-energy regions. Setting appropriate discrimination thresholds for the detectors helps reject events unrelated to single neutron scattering on hydrogen, thereby improving the accuracy of the reconstructed spectrum. This improvement is verified through simulations and experimentally measured spectra for neutrons from an AmBe source with energies above 5.5 MeV. The technique is expected to facilitate the measurement of neutrons with energies above 10 MeV from an accelerator-driven source in a relatively simple and reliable manner.