Erlangen 2018 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 33: Poster Session II
A 33.30: Poster
Mittwoch, 7. März 2018, 16:15–18:15, Redoutensaal
Gamma spectroscopy to measure the 229Th isomer energy using a 2-dimensional array of metallic magnetic microcalorimeters — •J. Geist1, D. Hengstler1, M. Krantz1, R. Pons1, P. Schneider1, C. Schötz1, S. Kempf1, L. Gastaldo1, A. Fleischmann1, C. Enss1, G.A. Kazakov2, S.P. Stellmer2, T. Schumm2, and J. Bussmann1 — 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 results of the latest measurements with an adjusted maXs-30 detector, new generation SQUIDs and an updated setup in the cryostat.