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HK: Physik der Hadronen und Kerne

HK 10: Poster Session: Nuclear Physics/Spectroscopy

HK 10.29: Poster

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

Decay spectroscopy of the N=Z+1 nucleus ⁷⁹Y — •J. Döring — GSI, Darmstadt, Germany

In the mass 80 region, the occupation of the intruder d_5/2 and high-j g_9/2 orbitals in the proton-rich odd-mass strontium and yttrium nuclei drives these nuclei to large prolate deformation which is stabilised by the Z=38 gap in the single-particle energies. This gives rise to low-lying collective states which may be populated in β decay. To search for such states, the β⁺/EC ground-state decay of the odd-proton N = Z + 1 nucleus ⁷⁹Y has been studied. The ⁷⁹Y nuclei were produced by using the ⁴⁶Ti(⁴⁰Ca,α p2n) reaction and investigated as mass-separated and chemically clean beams of ⁷⁹Y¹⁹F⁺ ions by means of the ISOL facility of GSI Darmstadt. The fluorination method yielded a very efficient suppression of unwanted reaction products.

Positrons and β-delayed γ rays were measured by using a plastic-scintillator and composite germanium detectors, respectively. The known ⁷⁹Y decay scheme [1,2] was extended by about 20 new γ transitions based on β-γ-γ coincidence relations. Some of the ⁷⁹Sr states were identified to form a rotational-like decay sequence feeding into the 1/2⁺[431] Nilsson bandhead state at 375 keV which is known from an in-beam study [3]. Quasiparticle-triaxial-rotor calculations indicate that a well-deformed prolate shape is necessary to reproduce the experimental excitation energies of this positive-parity sequence.

[1] H. Grawe et al., Z. Phys. A 341, 247 (1992).

[2] J. Mukai et al., Z. Phys. A 342, 393 (1992).

[3] S. Suematsu et al., Kyushu Univ., Tandem Acc. Lab. (1991) p. 72.