IMPROVEMENT IN CODED-APERTURE IMAGE QUALITY USING CONTINUOUS
MASK ROTATION

Holdup is the residual nuclear material inside process equipment at nuclear facilities and it is routinely measured for materials accounting and criticality safety. However, quantitative material estimates derived from these measurements are subject to significant error due to the unknown distribution of material inside. Although not widely used, portable gamma cameras are useful tools for this application because they can resolve the location and shape of nuclear materials, potentially providing material quantities directly from the image. Coded-aperture imagers can efficiently image low-energy gamma emissions with high resolution and the ideal response is a delta-function. However, the measured response is generally nonuniform and subject to irregularities that can significantly bias the result. Traditional coded-aperture masks are static during a measurement, or switch discretely between mask and antimask configurations, but continuous motion has been shown to significantly increase image SNR by averaging out image artifacts. In this work, we investigate the use of continuous mask rotation for the H420, a commercial CZT-based imager. A two-fold improvement in point-source SNR was shown for continuous rotation versus conventional mask-antimask switching. Results for both MURA- and HURA-based mask patterns are reported along with images of several HEU samples.