# 18th International Workshop on Low Temperature Detectors (LTD-18)

22-26 July 2019
Milano
Europe/Rome timezone

## γ-ray measurements of Th-229 isomer using TES microcalorimeters

25 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

### Piazza Città di Lombardia

#### Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector Applications

Haruka Muramatsu

### Description

The lowest energy of $^{229}$Th isomeric state is widely known to be around 10 eV and by utilizing this level, a nuclear clock may be realized. The $^{229}$Th nuclear clock is expected to have an enhanced sensitivity to the time variation of the fine structure constant.
To realize the clock, we need to determine the lowest-energy of the $^{229}$Th isometric state precisely. The approach to measure the energy level is utilizing the energy difference of the doublet lines at 29.19 keV.
We developed TES microcalorimeters for this measurements and measured the emission lines of $^{229}$Th decayed from $^{233}$U. In the first campaign conducted in 2017, the energy resolution of the TES microcalorimeter degraded to 40 eV at 26 keV in the measurement environment. Thus the doublet was not resolved in the spectrum. We estimated the isomer energy level using the decay chain starting from 97.1 keV. Then we improved the detector system and recently confirmed an energy resolution of 18 +/-4 eV FWHM at 26 keV in the environment to measure $^{229}$Th. We report the first results from the campaign in 2017 and the improvement of the detector.

Student (Ph.D., M.Sc. or B.Sc.) N Y

### Co-authors

Dr Tasuku Hayashi (JAXA/ISAS) Mr Naoki Yuasa (Kyushu University) Dr Atsushi Yamaguchi (RIKEN) Prof. Kazuhisa Mitsuda Prof. Noriko Yamasaki (JAXA) Prof. Keisuke Maehata (Kyushu University) Dr Hidetoshi Kikunaga (Tohoku University) Ms Misaki Takimoto (JAEA) Dr Keisuke Nakamura (JAEA)

### Presentation Materials

 LTD18_poster_muramatsu3.pdf LTD18_presen_muramatsu.pdf