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Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 28: Spectroscopy: 70 ≤ A < 110

HK 28.7: Gruppenbericht

Dienstag, 17. März 1998, 15:45–16:15, D

Measurement of ps-lifetimes in the semi-magic nuclei 95Rh and 94Ru with the EUROBALL Cluster detectors — •Andrea Jungclaus1, Dietrich Kast1, Klaus-Peter Lieb1, Christian Teich1, Matthias Weiszflog1, Thomas Härtlein2, Christoph Ender2, Frank Köck2, Dirk Schwalm2, Jens Reif3, Jürgen Eberth4, Heinz-Georg Thomas4, Rüdiger Peusquens4, Alfred Dewald4, and Hubert Grawe51II. 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 — 4Institut für Kernphysik, Universität zu Köln, Zülpicherstrasse, D-50937 Köln — 5GSI, 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 (p1/2,g9/2) space. In contrast, states with spins higher than 12+, 13 in 94Ru and 25/2+, 25/2 in 95Rh are generated by raising a neutron from the g9/2 across the N=50 shell gap into the d5/2 orbit [1]. Due to the large shell gap of about 2.5 MeV, these neutron particle-hole excitations decay via high-energy γ-rays. The main goal of our investigation was to measure the strengths of these ’single-particle’ transitions across the N=50 shell closure and to compare them to detailed shell model calculations within the (p1/2, g9/2, d5/2) configuration space.
Because of their high efficiency for the detection of high-energy γ-ray, the EUROBALL Cluster detectors are perfectly suited for our purposes. We used six of these detectors, a 145 MeV 40Ca beam from the MP accelerator at the MPI Heidelberg and a 58Ni target foil to determine lifetimes in the range from 1-50 ps in the 3p and 4p reaction channels 95Rh and 94Ru via the RDDS method. The high statistics of these data allows us to address the advantages and disadvantages of various methods to analyse such coincidence RDDS data, namely the analysis of R(d) functions determined in coincidence with transitions above and below the transition of interest, and the DDCM method [2]. Only the richness of complementary information enabled us to reveal sources of systematic errors and to deduce reliable values for lifetimes and uncertainties.

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

[2] G. Böhm et al., Nucl. Instr. Meth. A329 (1993) 248

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