Speaker
Description
Potassium-40 ($^{40}$K) is a long-lived, naturally occurring radioactive isotope. It decays primarily by beta emission to calcium, and by electron-capture to an excited state of argon. An additional electron-capture to the ground state of argon theoretically exists, but has never been previously measured. Predicted intensities for this branch are highly variable (0-0.8%) and this decay channel impacts our understanding of nuclear structure and geochronological dating. Additionally, this decay acts as a challenging background for many rare-event searches, especially those involving NaI-based scintillators (ex. ANAIS-112, COSINE-100, COSINUS, DAMA/LIBRA, and SABRE) because of the 3 keV events produced from the electron capture that resides directly in their signal region. KDK (Potassium (K) Decay (DK)) is an international collaboration that has performed the first measurement of this branching ratio. The experiment is performed using a silicon drift detector with a thermally deposited, enriched $^{40}$K source inside the Modular Total Absorption Spectrometer (MTAS, Oak Ridge National Laboratory). MTAS is a large NaI detector whose high gamma-ray efficiency enables the proper discrimination between ground and excited state electron capture events. Our measurement yields a ground state branching ratio of 0.098% $\pm$ 0.023% (stat) $\pm$ 0.010% (syst). We report on the KDK experimental analysis and the extensive implications of our measurements.
| Submitted on behalf of a Collaboration? | Yes |
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