title: Prospects for measuring the229Th isomer energy using a metallic magnetic microcalorimeter.
abstract: The Thorium-229 isotope features a nuclear isomer state with an extremely low energy. The currently most accepted energy value, 7.8±0.5 eV, was obtained from an indirect measurement using a NASA x-ray microcalorimeter with an instrumental resolution 26 eV. We study, how state-of-the-art magnetic metallic microcalorimeters with an energy resolution down to a few eV can be used to measure the isomer energy. In particular, resolving the 29.18 keV doublet in the γ-spectrum following the α-decay of Uranium-233, corresponding to the decay into the ground and isomer state, allows to measure the isomer transition energy without additional theoretical input parameters, and increase the energy accuracy. We study the possibility of resolving the 29.18 keV line as a doublet and the dependence of the attainable precision of the energy measurement on the signal and background count rates and the instrumental resolution.
authors.affiliation: Wolfgang Pauli Institute, Univ. Wien - UZA 4 Nordbergstrasse 15, A, 1090 Vienna, Austria ; Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: G A
authors.initials: GA
authors.lastname: Kazakov
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: V
authors.initials: V
authors.lastname: Schauer
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Schwestka
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: S P
authors.initials: SP
authors.lastname: Stellmer
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: J H
authors.initials: JH
authors.lastname: Sterba
authors.affiliation: Kirchhoff-Institute for Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Fleischmann
authors.affiliation: Kirchhoff-Institute for Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Gastaldo
authors.affiliation: Kirchhoff-Institute for Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Pabinger
authors.affiliation: Kirchhoff-Institute for Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Enss
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Schumm
keywords: Design of experiment; Gamma spectroscopy; Isomer energy; Thorium-229
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