Impact of embedded ${}^{163}$Ho on the performance of the transition-edge sensor microcalorimeters of the HOLMES experiment

Abstract

We present a detailed investigation of the performance of transition-edge sensor (TES) microcalorimeters with ${}^{163}$Ho atoms embedded by ion implantation, as part of the HOLMES experiment aimed at neutrino mass determination. The inclusion of ${}^{163}$Ho atoms introduces an excess heat capacity due to a pronounced Schottky anomaly, which can affect the detector's energy resolution, signal height, and response time. We fabricated TES arrays with varying levels of ${}^{163}$Ho activity and characterized their performance in terms of energy resolution, decay time constants, and heat capacity. The intrinsic energy resolution was found to degrade with increasing ${}^{163}$Ho activity, consistent with the expected scaling of heat capacity. From the analysis, we determined the specific heat capacity of ${}^{163}$Ho to be $(2.9\pm 0.4(\mathrm{stat})\pm 0.7(\mathrm{sys}))$ J/K/mol at $(94\pm 1)$\,mK, close to the literature values for metallic holmium. No additional long decay time constants correlated with ${}^{163}$Ho activity were observed, indicating that the excess heat capacity does not introduce weakly coupled thermodynamic systems. These results suggest that our present TES microcalorimeters can tolerate ${}^{163}$Ho activities up to approximately 5 Bq without significant performance degradation. For higher activities, reducing the TES transition temperature is necessary to maintain energy resolution. These findings provide critical insights for optimizing TES microcalorimeters for future neutrino mass experiments and other applications requiring embedded radioactive sources. The study also highlights the robustness of TES technology in handling implanted radionuclides while maintaining high-resolution performance.

Published on The European Physics Journal C

References in corpus (7)

• HOLMES - The Electron Capture Decay of 163Ho to Measure the Electron Neutrino Mass with sub-eV sensitivity
• Limits on the Existence of sub-MeV Sterile Neutrinos from the Decay of ${}^7$Be in Superconducting Quantum Sensors
• Statistical sensitivity of 163-Ho electron capture neutrino mass experiments
• Working principle and demonstrator of microwave-multiplexing for the HOLMES experiment microcalorimeters
• Most stringent bound on electron neutrino mass obtained with a scalable low temperature microcalorimeter array
• Investigation of peak shapes in the MIBETA experiment calibrations
• A lab scale experiment for keV sterile neutrino search

Cited by in corpus (1)

• Phenomenological Modeling of the ${}^{163}$Ho Calorimetric Electron Capture Spectrum from the HOLMES Experiment