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HK: Fachverband Hadronen und Kerne

HK 67: Poster Session

HK 67.58: Poster

Thursday, March 19, 2009, 14:00–16:00, Audi-Max

Long-lived isomeric states in neutron-deficient thorium isotopes? — •Johannes Lachner, Iris Dillmann, Thomas Faestermann, Gunther Korschinek, Mikhail Poutivtsev, and Georg Rugel — Technische Universität München

In a recent publication Marinov et al. (Phys. Rev. C 76, 021303(R), 2007) reported that isomeric states should exist in the neutron-deficient thorium-isotopes ²¹¹Th, ²¹³Th, ²¹⁷Th and ²¹⁸Th. These isotopes were found by use of a conventional mass spectrometer in abundances of 10⁻¹¹ relative to ²³²Th in a natural sample of thorium. Therefore they should be of primordial origin and have minimum half-lives of several 100 million years. This is surprising, as the ground-states of these α-emitters have lifetimes shorter than seconds and are surrounded by other short-lived α-emitting nuclei. So their production and half-life can not be explained within current models of nuclear and astrophysics. With the method of Accelerator Mass Spectrometry (AMS) at the Maier-Leibnitz-Laboratory in Munich this search could be repeated with higher sensitivity and complete reduction of background due to molecules. Hereby none of the four neutron-deficient thorium isotopes could be detected, the new upper limit for their abundance is an order of magnitude below the postulated value. The work was supported by DFG through EXC 153.