A fully-automated, liquid-moderated neutron spectrometer system

A novel, water-based, neutron spectroscopy system has been designed, simulated, and tested at the National Research Council of Canada. The active part of the detection system is a small proportional counter sensitive to thermal neutrons. The proportional counter is suspended along the symmetry axis of a large, rectangular water bath, and can be positioned remotely anywhere along this axis down to the bottom face. Measured count rates as a function of depth of the counter for both an americium-beryllium and a californium-252 neutron source demonstrate the ability of the system to discriminate between sources with different energy spectra. An MCNP6 simulation of an AmBe source agrees with the data within uncertainties at the 2%-level and is used to construct the response functions of the spectrometer system. Unfolded energy spectra are determined using an analysis of the singular value decomposition of the response matrix. Finally, a Monte Carlo study of the system indicates an ability to measure the fluence rate of the radionuclide sources.