SPECTRUM ISOLATION IN MULTI-SOURCE IMAGE RECONSTRUCTION USING A DUAL-PARTICLE IMAGER

Year
2015
Author(s)
P. Marleau - Sandia National Laboratories
S. D. Clarke - University of Michigan
M. Flaska - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
S. A. Pozzi - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
Michael C. Hamel - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
John K. Polack - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
Abstract
A dual-particle imager (DPI) has been developed at the University of Michigan that is capable of detecting photons and neutrons. The DPI can estimate the spatial distribution and photon and neutron energy spectra of present radioactive sources by using the principles of Compton scattering and neutron elastic scattering. When multiple sources are present, it is desirable to determine the photon and neutron energy spectra for specific regions of interest within the field of view (FOV). A maximum-likelihood expectation-maximization (MLEM) approach was used to reconstruct the spatial distribution and simultaneously unfold the energy spectra for each spatial pixel. The MLEM algorithm utilizes a system matrix computed with the Monte Carlo transport code MCNPX-PoliMi. The response of the DPI to an emitted neutron spectrum (ranging from 0-10 MeV) and an emitted photon spectrum (ranging from 0-5 MeV) was simulated at 5° increments over a 2p FOV. A bin-mode system response matrix, which accounted for energy in both observation and source dimensions, was constructed from the simulated responses. This paper describes how this method isolates the energy spectra for each individual source in a multi-source field. Image reconstruction and spectrum isolation results will be shown for a multi-source measurement of 252Cf and 60Co.