Freiburg 1999 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 19: Kernphysik III / Magnetische Momente

HK 19.1: Gruppenbericht

Dienstag, 23. März 1999, 14:00–14:30, B

Lifetime and magnetic moment measurements in the shell model nucleus ₄₄⁹⁴Ru — •A. Jungclaus¹, D. Kast¹, K.P. Lieb¹, C. Teich¹, M. Weiszflog¹, T. Härtlein², C. Ender², F. Köck², D. Schwalm², J. Reif³, I.P. Johnstone⁴, J. Eberth⁵, H.G. Thomas⁵, R. Peusquens⁵, A. Dewald⁵, H. Grawe⁶, and M. Górska⁶ — ¹II. Physikalisches Institut, Universität Göttingen, Bunsenstr. 7-9, D-37073 Göttingen — ²Max-Planck-Institut für Kernphysik, D-69029 Heidelberg — ³Institut für Kern- und Hadronenphysik, FZ Rossendorf, D-01314 Dresden — ⁴Department of Physics, Queen’s University, Kingston, Canada — ⁵Institut für Kernphysik, Universität zu Köln, Zülpicherstrasse, D-50937 Köln — ⁶GSI, Darmstadt

In the semi-magic N=50 nuclei ₄₄⁹⁴Ru and ₄₅⁹⁵Rh, the low-energy parts of the excitation schemes reflect the various valence proton configurations within the (p_1/2,g_9/2) space. In contrast, states with spins higher than 12⁺, 13⁻ in ⁹⁴Ru and 25/2⁺, 25/2⁻ in ⁹⁵Rh are assumed to be generated by raising a neutron from the g_9/2 across the N=50 shell gap into the d_5/2 orbit [1]. To prove these predictions and to further investigate the role of the lower-lying orbits (f_5/2, p_3/2) in the intermediate spin range precise lifetimes in the range from 0.5 to 40 ps were determined in both nuclei by means of the RDDS technique and the reaction ⁵⁸Ni + ⁴⁰Ca at 145 MeV. Whereas the results for ⁹⁵Rh have already been presented in [2], we will report here on the experimental electromagnetic transition strengths obtained for ⁹⁴Ru. Both the excitation energies and transition rates are compared to large-scale shell model calculations using different configuration spaces and residual interactions [2,3]. At negative parity, the experimental 13₂⁻, 14₁⁻, and 15₁⁻ states could be identified as pure proton states with the configuration π(g_9/2)⁵ π(f_5/2). The agreement between experiment and calculations is excellent. Furthermore, it was found that due to the particle-hole symmetry within the g_9/2 shell, the structure of the π=- yrast states in ⁹⁵Rh is equivalent to that of the corresponding π=+ levels in ⁹⁴Ru plus a p_1/2 proton [ ⁹⁵Rh⁻ = ⁹⁴Ru⁺ ⊗ π(p_1/2) ] and vice versa. To complete the experimental information in the two N = 50 nuclei, g-factors of excited states with lifetimes between 20 ps and 1 ns were determined via the IMPAD method after recoil implantation into ferromagnetic Fe and Ni hosts. Both experiments reported on have been performed at the MPI Heidelberg.

[1] H. A. Roth et al., Phys. Rev. C50 (1994) 1330.

[2] A. Jungclaus et al., Nucl. Phys A637 (1998) 346.

[3] I. P. Johnstone and L. D. Skouras, Phys. Rev. C55 (1997) 1227.