Measurement of neutron fluence spectra up to 150 MeV using a stacked scintillator neutron spectrometer

Abstract

A stacked scintillator neutron spectrometer (S3N) consisting of three slabs of liquid organic scintillator is described. A pulsed beam providing a broad spectrum of neutron energies is used to determine the detection efficiency of the spectrometer as a function of incident neutron energy and to measure the pulse height response matrix of the system. Neutron spectra can then be determined for beams with any kind of time structure by unfolding pulse height spectra measured by the S3N. Examples of fluence spectrum measurements in the energy range 20-150 MeV are presented.

Scintillation Detectors for Fast Neutrons

“…Spectral neutron fluences were determined by means of tof-spectrometry and, independently, by unfolding the simultaneously measured pulse height spectra. Excellent agreement was achieved [91] between the results obtained by the two different methods, thus demonstrating that pulse-height unfolding is a viable method for determining spectral neutron fluence up to 150 MeV.…”

“…Essentially the same principle was applied for neutron spectrometry, both by means of tofmeasurements as well as by unfolding of pulse height spectra, in the energy range from 50 MeV to 150 MeV [90,91]. Correlated signals of two or three liquid scintillators, each 7 cm in thickness and closely stacked, were analysed using pulse shape discrimination to reject gammaevents.…”

Quasi-monoenergetic high-energy neutron standards above 20 MeV

“…This can be avoided by enlarging scintillator sizes but this approach will also deteriorate the resolution in TOF measurements. Stacked liquid scintillators were developed to minimize the escape of forward recoil protons and to reproduce ideal pulse height spectra as if all protons caused stopped events [55,56]. 238 U fission chambers are constructed as a stack of several electrodes with fissile deposits to achieve sufficient neutron sensitivity.…”