N. Hines | Searcharxiv

arXiv2025

Magneto-$\nu$: Heavy neutral lepton search using $^{241}$Pu $\beta^-$ decays

The MAGNETO-$\nu$ experiment searches for keV-scale heavy neutral leptons (HNLs) through precise measurements of the $\beta^-$-decay spectrum of $^{241}$Pu. We present spectra comprising a total of 194 million $\beta^-$ decays recorded using decay energy spectrometry with metallic magnetic calorimeters, representing the most statistically precise measurement of $^{241}$Pu $\beta^-$ decay to date. The $\beta$-endpoint energy was determined using $\gamma$ rays and X rays from an external $^{133}$Ba calibration source, yielding $Q_\beta = 22.273\,(33)$\,keV. The measured spectrum shows no statistically significant deviation from the allowed $\beta$-decay model. From a subset of the high-statistics data, we set an upper limit on the mixing of an 11.5-keV HNL with the electron neutrino, $|U_{e4}|^2 < 1.31 \times 10^{-3}$ at the 95\% confidence level.

hep-ex↗

arXiv2024

Decay Energy Spectrometry for Improved Nuclear Material Analysis at the IAEA NML

Decay energy spectrometry (DES) is a novel radiometric technique for high-precision analysis of nuclear materials. DES employs the unique thermal detection physics of cryogenic microcalorimeters with ultra-high energy resolution and 100$\%$ detection efficiency to accomplish high precision decay energy measurements. Low-activity nuclear samples of 1 Bq or less, and without chemical separation, are used to provide elemental and isotopic compositions in a single measurement. Isotopic ratio precisions of 1 ppm - 1,000 ppm (isotope dependent), which is close to that of the mass spectrometry, have been demonstrated in 12-hour DES measurements of ~5 Bq samples of certified reference materials of uranium (U) and plutonium (Pu). DES has very different systematic biases and uncertainties, as well as different sensitivities to nuclides, compared to mass-spectrometry techniques. Therefore, the accuracy and confidence of nuclear material assays can be improved by combining this new technique with existing mass-spectrometry techniques. Commercial-level DES techniques and equipment are being developed for the implementation of DES at the Nuclear Material Laboratory (NML) of International Atomic Energy Agency (IAEA) to provide complementary measurements to the existing technologies. The paper describes details of DES measurement methods, as well as DES precision and accuracy to U and Pu standard sources to discuss its capability in analysis of nuclear safeguards samples.

physics.ins-det↗