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A: Fachverband Atomphysik

A 20: Poster Session I

A 20.36: Poster

Dienstag, 7. März 2017, 17:00–19:00, P OG1

Gamma spectroscopy to measure the ²²⁹Th isomer energy using a 2-dimensional array of metallic magnetic microcalorimeters — •P. Schneider¹, D. Hengstler¹, J. Geist¹, M. Krantz¹, C. Schötz¹, S. Kempf¹, L. Gastaldo¹, A. Fleischmann¹, C. Enss¹, G.A. Kazakov², S.P. Stellmer², and T. Schumm² — ¹Heidelberg University — ²Vienna University of Technology

The isotope ²²⁹Th has a nuclear isomer state with the lowest presently known excitation energy, which possibly allows to connect the fields of nuclear and atomic physic with a potential application in a nuclear clock. In order to verify and improve the accuracy of the currently most accepted energy value, (7.8±0.5) eV, we want to resolve the 29.18 keV doublet in the γ-spectrum following the α-decay of ²³³U, corresponding to the decay into the ground and isomer state, to measure the isomer transition energy without additional theoretical input parameters.

We developed the detector array maXs-30 consisting of 8x8 metallic magnetic calorimeters with an expected energy resolution below 6 eV, providing a large detection area of 16 mm² to face the low rate of the 29.18 keV transitions.

In first measurements we observed the 29.18 keV transitions as a single peak with an instrumental resolution of 33 eV. A strong background contribution due to β-radiation from accumulated decay products in the ²³³U-source was discovered. We present the experimental setup and the obtained results. We discuss the present sensitivity to the isomer energy and how this will improve in a next experiment based on a cleaned source and dc-SQUIDs with improved flux noise.