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MS: Fachverband Massenspektrometrie

MS 3: Studies of Nuclear Metastable States

MS 3.1: Invited Talk

Tuesday, March 15, 2022, 10:30–11:00, MS-H9

Two-photon decay of nuclear isomers — •Wolfram Korten — IRFU, CEA, Université Paris-Saclay

The nuclear two-photon decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. First order processes usually dominate the decay by many orders of magnitude, but two-photon emission may become significant when first order processes are forbidden or strongly retarded. This is the case for nuclei with a first excited 0+ state, since the emission of a single gamma ray is strictly forbidden for the resulting electric monopole transition to the 0+ ground by angular momentum conservation. Such a configuration occurs when the potential energy of the nucleus is characterized by local minima for different shapes. If the potential barrier separating the secondary minimum from the ground-state minimum is sufficient strong the excited 0+ state will become a long-lived state, a so-called shape isomer.

The first successful observation of a nuclear two-photon decay was achieved in the 1980s by a direct detection of the simultaneously emitted gamma-rays. However, the very small branching ratio with respect to other decay paths, such as internal conversion, becomes minuscule when searching for low-lying 0+ states below ~1 MeV. In this talk I will present an alternative method to directly search for such isomers by using time-resolved mass spectrometry at relativistic energies, where the atomic nucleus is completely stripped of its atomic electrons and report on the first successful experiment to directly observe the decay from an isomer in 72Ge at the GSI Experimental Storage Ring (ESR).