Enhancement of 3He ion chamber spectrometry with a pulsed neutron source

As it was found in previous study, presence of the thermal peak in neutron spectra measured by the ³He ionization chamber, makes it difficult to use its complete response function in unfolding process. In order to significantly reduce the thermal peak counting rate, an active method of rejecting low energy neutrons (< 100 eV) based on their time of flight has been developed and tested. The method required a modification of the proton accelerator beam line to produce short pulses of protons. A custom made 2-D acquisition system was also built and used to evaluate the pulsed beam system and compare its results with that obtained by a commercial DSP unit. It was found that the fast-to-thermal ratio can be improved by a factor of approximately 5.