Improving the Understanding of Gadolinium for use in Neutron Detectors

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Gadolinium has a very high neutron capture cross section, particularly isotopes Gd-155 and Gd-157 and produces a very high energy upon emission of a gamma cascade (~8MeV). However, this model for decay is not well understood, so we hope to improve this model via both computational and experimental methods. We hope to achieve a good model for the gadolinium mechanism of thermal neutron capture; this improved understanding will lead to better neutron detection via event identification and background discrimination. Neutron detectors that employ Gadolinium (Gd) as the neutron capture agent can be enhanced by improving the understanding of the subsequent gamma cascade of the neutron capture on Gd. This would open up a new area of development where the neutron has the potential to be (partially) tagged, resulting in better background discrimination. This is particularly useful in large area detectors where intrinsic radiation in the scintillator or the photo-sensor itself is a large source of background, enabling new deployment scenarios. Gd has an extremely large thermal neutron capture cross-section, second only to the capture cross-section of Xenon. The neutron capture on Gd has a Q-value of 8-MeV resulting in an associated gamma-ray cascade.Gd(n, gamma) interactions have been studied and the integrated spectrum is known, but the individual decay modes have not been measured. The 4-gamma mode is dominant, although these are not measured to be discrete energies and it is not known if the energy of the four gammas is equal to the Q-value of the decay (8 MeV). Given the available energy there is likely to be multiple sub-MeV cascades. The PhD will calculate and measure the gamma spectrum, hence determining what is missing in each detected event and allowing the events to be tagged.