Hannover 2020 – scientific programme
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A: Fachverband Atomphysik
A 14: Poster Session - Atomic Physics II
A 14.20: Poster
Tuesday, March 10, 2020, 16:00–18:00, Empore Lichthof
A new value for the isomer energy of 229Th, determined by high-resolution γ-spectroscopy with metallic magnetic micro-calorimeters — D. Hengstler1, J. Geist1, S. Allgeier1, M. Arndt1, M. Friedrich1, S. Kempf1, L. Gastaldo1, A. Fleischmann1, C. Enss1, S. Stellmer2, T. Schumm3, C. Düllmann4, and •P. Kuntz1 — 1Heidelberg University — 2University of Bonn — 3Vienna University of Technology — 4Mainz 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 a potential application in a nuclear clock. However, in order to excite this very narrow transition from the ground state to the isomer state with a laser a precise knowledge of the transition energy is needed. A detector with good energy resolution allows to deduce this transition energy from a high-statistic γ-spectrum of 229Th originating from the α-decay of 233U.
To improve the accuracy of the currently most accepted value of (7.8±0.5) eV, we developed and fabricated the detector array maXs-30 consisting of 8×8 metallic magnetic calorimeters. The detector features a large active detection area of 4 mm× 4 mm to face the low rate of the relevant γ-transitions, a world-record energy resolution Δ EFWHM < 10 eV up to 60 keV as well as a very small non-linearity and reliable energy calibration.
We present our latest 229Th spectrum measured with a purified 233U source and derive a trustful value for the isomer energy on different ways, leading to a result of Eiso = (8.09±0.13(stat)+0.05
−0.14(syst)) eV.