Daniel Bruno McDevitt

Detective quantum efficiency of an energy resolving photon counting detector

The output response characteristics of an X-ray photon counting detector are measured experimentally and simulated using a Monte Carlo method in order to quantify the loss of statistical information due to pile-up. The analysis is applied to idealize counting detector models, but is adaptable to realistic event processing that is not amenable to analytic solution. In particular, the detective quantum efficiency (DQE) is calculated as a function of flux rate and shown to have an intermediate zero for the paralyzable case at the maximum periodic rate. The progressive degradation of the spectral response as a function of increasing flux rate is also modeled. Analogous metrics to DQE are defined in regards to the detectors ability to resolve atomic number and enhance image contrast based on atomic number differentiation. Analytic solutions are provided for the output and linearized response statistics and these interpolate well across the Monte Carlo and experimental results.

3He neutron detector design for active detection of cargo containers

We report on the design of a neutron detector using industry standard 3He tubes to count delayed neutrons during the interrogation of cargo containers for the presence of Special Nuclear Material (SNM). Simulations of the detector design were run for delayed neutron spectra for a variety of cargos containing SNM using the Monte Carlo computer code COG. The simulations identified parameters crucial to optimize the detector design. These choices include moderating material type and thickness, tube spacing, tube pressure and number of tubes. An experimental prototype was also constructed based on the simulated design specifications. This paper discusses the parameters that lead up to the optimized detector design. It also compares the performance of the Monte Carlo simulated design and the experimental detector when exposed to a 239Pu-Be source.

A new integrated neutron/gamma radioisotope identification device evaluated under mixed radiation fields

Hand-Held RadioIsotope Identification Devices (HHRIID) are defined as a new class of portable neutron/gamma radiation detectors with specifications presented in the ANSI Standards N42.33 and N42.34. We have proposed a novel HHRIID design concept which uses a single photosensor to detect light emitted by two optically separated scintillator materials, one optimized for gamma detection and the other optimized for neutron detection. This work describes the performance of a modified charge integration discrimination method developed to test the viability of the new design. The scintillators chosen for the experiment were LYSO and ZnS:Ag/LiF.