Decay Energy Spectroscopy of Radionuclides With Magnetic Microcalorimeters

Alexander Kavner, University of Michigan

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Magnetic Microcalorimeters (MMCs) are cryogenic detectors consisting of an absorber, a paramagnetic sensor, and superconducting pick-up coils and are utilized for high resolution radiation and particle detection. MMCs have been previously employed as gamma ray sensors and have demonstrated far superior resolution than traditional HPGe detectors. We are developing MMC-based decay energy spectrometry (DES) techniques for high accuracy measurements of absolute activities of radioactive materials. Nuclear samples are fully embedded within a gold foil absorber that is in thermal contact with the MMC. Decay radiation in the form of alphas, conversion electrons, betas, nuclear recoils, and low energy photons are absorbed and thermalized within this foil with 100% efficiency, producing spectra with single peak(s) at the total decay energy of each isotope. The total number of decays and absolute activities can be obtained by integrating the decay energy peaks. Using this technique, we measured the absolute activities of 146Sm and 147Sm samples with known masses to improve the accuracy of their half-life-values. This is of importance as Sm-Nd chronometry is used to date various planetary materials and constrain the sequence of early Solar-System events. We present initial experimental and analysis results on the absolute decay counting of 146Sm and 147Sm samples. This DES technique is of interest to the IAEA and broader nuclear safeguards and non-proliferation community as samples can be rapidly processed and nuclear isotopic contents identified with no chemical separation necessary. We have performed initial test forensics measurements and identified Plutonium, Uranium, Americium, etc. in a “mystery” sample provided by LLNL radiochemistry. Decay energy spectroscopy is a promising technique for both fundamental nuclear science as well as the safeguards community.

Abstract Author(s): A.R.L. Kavner, Q. Shollenberger, K. Kmak, S.T.P. Boyd, O.B. Drury, S. Friedrich, I. Jovanovic, G.B. Kim