Heidelberg 2015 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 66: Structure and Dynamics of Nuclei 13

HK 66.3: Vortrag

Donnerstag, 26. März 2015, 17:30–17:45, T/SR19

Preparations for an optical access to the lowest nuclear excitation in ²²⁹Th ^* — •Lars v.d. Wense¹, Benedict Seiferle¹, Mustapha Laatiaoui², and Peter G. Thirolf¹ — ¹Ludwig-Maximilians-Universität München — ²GSI Helmholtzzentrum für Schwerionenforschung Darmstadt

The isomeric lowest excited nuclear level of ²²⁹Th has been indirectly measured to be 7.6±0.5 eV (163±11 nm)[1]. This low transition energy, compared to energies typically involved in nuclear processes, would allow for the application of laser-spectroscopic methods. Also considering the isomeric lifetime of the excited state (estimated to be 10³ to 10⁴ s), which leads to an extremely sharp linewidth of Δω/ω∼ 10⁻²⁰, the isomer becomes a strong candidate for a nuclear-based frequency standard. In order to directly detect the isomeric ground-state decay and improve the accuracy of its energy as a prerequisite for an all-optical control, ^229mTh is populated via a 2% decay branch in the α decay of ²³³U. The Thorium ions are extracted and cooled with the help of a buffer-gas stopping cell and an RFQ-cooler. In order to suppress accompanying α decay chain products other than ²²⁹Th, a quadrupole mass spectrometer (QMS) is used. Following the QMS, the Thorium isomeric decay is expected to be detectable. Internal conversion as well as photonic decay is probed via different detection techniques [2]. Latest results will be presented.
[1] B.R. Beck et al., PRL 98, 142501 (2007).
[2] L. v.d.Wense et al., JINST 8 P03005 (2013).
^* Supported by DFG Grant TH956/3-1.