Neutron Energy Spectrum Unfolding with Deuterium- and Hydrogen-based Liquid Scintillators

Neutron spectroscopy has direct application to the detection of special nuclear materials for nuclear safeguards and nonproliferation. Liquid scintillation detectors rely on partial energy deposition through elastic scattering of incident neutrons on H and C nuclei. Therefore, the relation between scintillation pulse-height and incident neutron energy is not unique, and incident neutron energy spectra must be unfolded from detector pulse-height spectra through the use of a response matrix. There is reason to believe that deuterated liquids will hold an advantage over standard hydrogen-based liquids for spectrum unfolding, due to the backward-peaked differential cross-section of n-d scattering. In this work, we compare spectrum unfolding performance between EJ309 (hydrogen-based) and EJ315 (deuterated). For the analysis, we use the Monte-Carlo code MCNP-PoliMi to calculate simulated response matrices and trial detector-response functions using continuous and discrete incident neutron spectra. Spectrum unfolding is performed using a sequential-least-squares algorithm. Our results support the anticipated advantage of deuterated liquids over standard hydrogen-based liquids for spectrum unfolding.