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TT: Fachverband Tiefe Temperaturen

TT 18: Superconductivity: Poster

TT 18.64: Poster

Montag, 18. März 2024, 15:00–18:00, Poster C

A dedicated 2-dimensional array of metallic magnetic microcalorimeters to resolve the 29.18 keV doublet of ²²⁹Th — A. Striebel, A. Abeln, S. Allgeier, •A. Brunold, J. Geist, D. Hengstler, D. Kreuzberger, A. Orlow, L. Gastaldo, A. Fleischmann, and C. Enss — Heidelberg University

The isotope ²²⁹Th has the nuclear isomer state with the lowest presently known excitation energy, which possibly allows to connect the fields of nuclear and atomic physics with the potential application as a nuclear clock. In order to excite this very narrow transition with a laser a precise knowledge of the transition energy is needed. Recently the isomer energy (8.338±0.024) eV [Kraemer et al., arXiv:2209.10276, 2022] could be precisely determined. To get valuable insights, we will improve our high-resolution measurement [Sikorsky et al., PRL 125, 2020] of the γ-spectrum following the α-decay of ²³³U. This decay partially results in excited ²²⁹Th with a nuclear state at 29.18 keV. Resolving the doublet, that in turn results from de-excitation to the ground and isomer state, respectively, would allow an independent measurement of the isomer energy as well as the branching ratio of both transitions. To resolve this doublet, a 2D detector array consisting of 8×8 metallic magnetic calorimeters (MMCs) was fabricated. MMCs are operated at mK temperatures and convert the energy of a single incident γ-ray photon into a temperature pulse which is measured by a paramagnetic temperature sensor. We discuss the detector properties, including an energy resolution of 3.1 eV (FWHM) at 5.9 keV and present first spectra of ²²⁹Th taken with this detector.