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The European Physical Journal A

, Volume 32, Issue 1, pp 5–9

First Online: 27 April 2007Received: 11 March 2007Accepted: 12 April 2007


Medium-spin, yrast excitations in the Cs nucleus, populated in the spontaneous fission of Cm, were observed for the first time. Cs was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The newly observed yrast cascade, built on the known 6 isomer at 80 keV, was successfully described by shell model calculations. Analogously to the I isotone, the 6 isomer in Cs has the \\ensuremath{\pi g {7-2} ^4 d {5-2} u f {7-2} {6^-}}\ dominating configuration and the 7 excitation, located 175 keV above, corresponds to the \\ensuremath{\pi g {7-2} ^3 d {5-2}^2 u f {7-2} {7^-}}\ as dominating configuration. Similarly as in I, changing the position of the d5-2 proton orbital improves the reproduction of the data. However, in Cs the energy of this orbital should be increased compared to its energy in Sb, to get the best description, in contrast to I and Sb, where it had to be decreased. The best reproduction of excitation energies in Cs is obtained assuming that the πd5-2 orbital in Cs is located about 100 keV higher than in Sb. These observations suggest that the lowering of the d5-2 s.p. energy in Sb is not a physical effect due to the appearance of a neutron skin, as proposed by other authors, but rather an artifact due to some deficiency of the input data used in the shell model calculations in the region of the doubly magic Sn core.

PACS.21.10.-k Properties of nuclei; nuclear energy levels 21.10.Tg Lifetimes 25.85.Ca Spontaneous fission 27.60.+j \\ensuremath{90 \leq A \leq 149}\ R. Krücken

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Autor: T. Rzaca-Urban - W. Urban - M. Saha Sarkar - S. Sarkar - J. L. Durell - A. G. Smith - B. J. Varley - I. Ahmad


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