A novel capture-gated neutron spectrometer.

This thesis presents work on the development of a novel capture-gated neutron detector. Lithium-gadolinium-borate, 6Li6Gd(11B03)3:Ce, dispersed as microcrystals within the plastic scintillator BC-490 is a promising material for accurate dosimetry in mixed n-gamma fields. Spectral information above ~1 MeV is obtained by capture gating proton recoil events in the plastic scintillator to subsequent capture in 6Li. Below ~ 1 MeV, isolated capture events in either gadolinium or 6Li give energy information in this region. Discrimination based on capture gating is used to reject false coincidences due to gamma rays or incorrectly gated neutron events. A detailed Monte Carlo model has been created in MCNPX that predicts the energy response of the LGB spectrometer in the capture-gated mode of operation. These simulations have been supplemented by several monoenergetic neutron irradiations at the NPL low scatter facility. Results of simulations and measurements show that unfolding methods are necessary to determine the incident neutron spectra. Unfolding of measurement data has been conducted for radionuclide sources such as 241Am-Be and in the maze of a medical linear accelerator. The detector is shown to be more successful in harder fields where there is a large component above 1 MeV