Novel Measurement of Samarium-146 Half-Life with Cryogenic Microcalorimeters*

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. We are developing MMC-based decay energy spectrometry (DES) techniques for high accuracy measurements of absolute activities of and isotopic composition of radioactive samples. Nuclear samples are fully embedded within a gold foil absorber in thermal contact with the MMC device. Decay radiation in the form of alphas, betas, conversion electrons, nuclear recoils, and low energy photons are absorbed and thermalized within this foil with near 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. We present novel measurements of the ¹⁴⁶Sm and ¹⁴⁷Sm half-lives with values derived from the DES technique. The systematics of the measurements have been rigorously studied and examined. The absolute decay counting technique is therefore readily applicable to other nuclear measurements.