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. This 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. The energy spectrum of any constant neutron field impinging on this face from below the detector may be reconstructed with this system by mapping the thermal neutron response as a function of distance from the face, and using singular value decomposition to deduce the energy distribution. Agreement between experimental data from americium-beryllium neutron sources and the Monte Carlo software MCNP5 is excellent. Monte Carlo techniques are used to test the energy spectrum reconstruction using singular value decomposition for americium-boron and americium-beryllium neutron spectra.