Münster 2002 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 10: Poster Session: Nuclear Physics/Spectroscopy

HK 10.24: Poster

Dienstag, 12. März 2002, 10:30–12:45, Foyer Chemie

First measurement of β-decay properties of the proton drip-line nucleus ⁶⁰Ga — •C. Mazzocchi — GSI, Darmstadt, Germany

Nuclei with N≃Z between the double shell closures ⁵⁶Ni and ¹⁰⁰Sn are of particular interest due to their special nuclear-structure features, including shape coexistence, the influence of the proton dripline, and the relevance to the astrophysical rp process. We used the ²⁸Si(³⁶Ar,p3n) reaction and the ISOL facility of GSI Darmstadt to investigate for the first time the β decay of ⁶⁰Ga [1]. Beta-delayed γ rays were studied by means of an array of a plastic scintillator and germanium detectors, whereas charged particles were recorded in silicon-detector telescopes. The half-life (T_1/2) was found to be 70±15 ms. In analogy to the mirror nucleus ⁶⁰Cu, spin and parity of 2⁺ were assigned to the β-decaying ⁶⁰Ga state. Based on the βγγ coincidence data, several ⁶⁰Zn levels were identified, including the isobaric analogue state at 4851.9±0.7 keV and a hitherto unobserved (2⁺₂) state at 2558.7±0.5 keV. The latter lies higher than in ⁶²⁻⁶⁶Zn, which may reflect the SU(3) structure beyond ⁵⁶Ni. By using Coulomb-displacement energy systematics, a semi-empirical proton separation energy (S_p) of 40±70 keV was derived for ⁶⁰Ga. The experimental results on T_1/2, S_p and the structure of ⁶⁰Zn levels will be dicussed in comparison with theoretical predictions, in particular those obtained from large-scale shell model calculations. Due to the small S_p value of ⁶⁰Ga, only a small fraction of the rp process flow runs through this nucleus, while its dominant part involves the β decay of ⁶⁰Zn.

[1] C. Mazzocchi et al., Eur. Phys. J. A 12, 269 (2001).