High-Precision Excited-State Nuclear Recoil Spectroscopy with Superconducting Sensors

TL;DR

This paper demonstrates high-resolution nuclear recoil spectroscopy using superconducting sensors, revealing detailed recoil spectra for nuclear decay, with implications for nuclear physics and beyond-standard-model searches.

Contribution

First high-resolution recoil spectroscopy of a single nuclear state using superconducting tunnel junction sensors, advancing detection capabilities at eV-scale energies.

Findings

Measured nuclear recoil spectra in $^7$Be decay.

Compared spectral broadening to models and simulations.

Implications for nuclear physics and dark matter searches.

Abstract

Superconducting sensors doped with rare isotopes have recently demonstrated powerful sensing performance for sub-keV radiation from nuclear decay. Here, we report the first high-resolution recoil spectroscopy of a single, selected nuclear state using superconducting tunnel junction (STJ) sensors. The STJ sensors were used to measure the eV-scale nuclear recoils produced in $^7$Be electron capture decay in coincidence with a 478 keV $\gamma$-ray emitted in decays to the lowest-lying excited nuclear state in $^7$Li. Details of the Doppler broadened recoil spectrum depend on the slow-down dynamics of the recoil ion. The measured spectral broadening is compared to empirical stopping power models as well as modern molecular dynamics simulations at low energy. The results have implications in several areas from nuclear structure and stopping powers at eV-scale energies to direct searches for dark matter, neutrino mass measurements, and other physics beyond the standard model.