Monte Carlo Studies of High Resolution Microcalorimeter Detectors

World record energy resolution (DeltaE ~ 25 eV) has recently been demonstrated for soft gamma-ray detectors using small radiation absorbing elements coupled to transition-edge sensors (microcalorimeters). Initial results were obtained with a 1 mm wide by 250 mum thick tin absorber. We are proceeding with construction of arrays of sensors and exploring other absorber materials. Monte Carlo tools, e.g. - GEANT4, are useful for exploring the design space and performance expectations for these arrays of microcalorimeters. In this work, we use simulations to quantify some important characteristics of this emerging technology in the hard X- and gamma-ray regime, such as the effective area and effect of absorber material and thickness. We also explore, through simulations, how these detectors might be used in some interesting applications, like passive assay of spent nuclear fuel from X-ray fluorescence.