Simulating Particle Transport Within a Microcalorimeter to Unfold the Detector Response

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Brown, Adam E.
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Houghton University
The measurement technique of Decay Energy Spectroscopy (DES) utilizes high-energy resolution (7.5±0.2 eV FWHM at 6539 eV) [1] low temperature microcalorimeters to measure the total energy of a decay from an embedded radioactive source. DES spectra are histograms of the total decay energy thermalized in the absorber. Some of this energy is lost, largely due to decay products escaping the absorber or energy stored in metastable states (the latter depends on source preparation and is not considered in this work). This results in a measurement of energy that is lower than the decay energy. The escape probability is not constant as a function of initial decay energy but is dependent on the absorber material and the source’s energy, type, location, and distribution—all of which form what we call the detector response. In this work, the response matrix for a microcalorimeter is built using EGSnrc—a Monte Carlo particle transport software—to simulate the energy deposition of a point source of monoenergetic beta particles ranging from 10 keV to 2 MeV. This response matrix may be used to deconvolve the detector response from a DES measurement so systematic uncertainty can be reduced. This will result in a more precisely known beta decay shape, important for fields such as nuclear medicine and testing theoretical descriptions of beta decay at low energies.
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