Development of holmium-163 electron-capture spectroscopy with transition-edge sensors

TL;DR

This paper reports the development of high-resolution microcalorimeters with transition-edge sensors for electron-capture spectroscopy of holmium-163, aiming to improve neutrino mass measurements by capturing decay energy with high precision.

Contribution

It introduces a complete process for producing, isolating, and measuring holmium-163 using advanced microcalorimeters with transition-edge sensors, advancing electron-capture spectroscopy techniques.

Findings

Successful development of transition-edge sensors for 163Ho spectroscopy

Measurement of the 163Ho electron-capture spectrum

Comparison of measured spectrum with theoretical models

Abstract

Calorimetric decay energy spectroscopy of electron-capture-decaying isotopes is a promising method to achieve the sensitivity required for electron neutrino mass measurement. The very low total nuclear decay energy (QEC < 3 keV) and short half-life (4570 y) of 163Ho make it attractive for high-precision electron capture spectroscopy (ECS) near the kinematic endpoint, where the neutrino momentum goes to zero. In the ECS approach, an electron-capture-decaying isotope is embedded inside a microcalorimeter designed to capture and measure the energy of all the decay radiation except that of the escaping neutrino. We have developed a complete process for proton-irradiation-based isotope production, isolation, and purification of 163Ho. We have developed transition-edge sensors for this measurement and methods for incorporating 163Ho into high-resolution microcalorimeters, and have measured the electron-capture spectrum of 163Ho. We present our work in these areas and discuss the measured spectrum and its comparison to current theory.