Development of decay energy spectroscopy for radio impurity analysis

TL;DR

This paper introduces a decay energy spectroscopy method using magnetic microcalorimeters to analyze radioactive impurities with high resolution, demonstrating its effectiveness in identifying decay chains relevant for low-background experiments.

Contribution

The development of a DES system with MMCs for radio-impurity analysis, achieving high energy resolution and successful identification of decay events in materials used for rare-event searches.

Findings

Achieved 45 keV energy resolution with the DES system.

Successfully identified decay chains of Ra-226 and Th-228.

Demonstrated long-term measurement capability over ten days.

Abstract

We present the development of a decay energy spectroscopy (DES) method for the analysis of radioactive impurities using magnetic microcalorimeters (MMCs). The DES system was designed to analyze radionuclides, such as Ra-226, Th-228, and their daughter nuclides, in materials like copper, commonly used in rare-event search experiments. We tested the DES system with a gold foil absorber measuring 20x20x0.05 mm^3, large enough to accommodate a significant drop of source solution. Using this large absorber and an MMC sensor, we conducted a long-term measurement over ten days of live time, requiring 11 ADR cooling cycles. The combined spectrum achieved an energy resolution of 45 keV FWHM, sufficient to identify most alpha and DES peaks of interest. Specific decay events from radionuclide contaminants in the absorber were identified. This experiment confirms the capability of the DES system to measure alpha decay chains of Ra-226 and Th-228, offering a promising method for radio-impurity evaluation in ultra-low background experiments.