Eur. Phys. J. A 15, 181-184 (2002)
DOI: 10.1140/epja/i2001-10250-8

The neutron and proton two-particle nucleus : New low-spin states observed in the decay of and an estimate of the energy of the isomer

A. Korgul¹, H. Mach², B. Fogelberg², W. Urban¹, W. Kurcewicz¹, T. Rzaca-Urban¹, P. Hoff³, H. Gausemel³, J. Galy², J.L. Durell⁴, W.R. Phillips⁴, A.G. Smith⁴, B.J. Varley⁴, N. Schulz⁵, I. Ahmad⁶, L.R. Morss⁶, M. Górska⁷, V.I. Isakov⁸, K.I. Erokhina⁹, J. Blomqvist¹⁰, F. Andreozzi¹¹, F. Coraggio¹¹, A. Covello¹¹ and A. Gargano<sup>11

1</sup>  Institute of Experimental Physics, Warsaw University, ul. Hoza 69, 00-681 Warszawa, Poland
²  Department of Radiation Science, Uppsala University, S-61182 Nyköping, Sweden
³  Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-00315 Oslo, Norway
⁴  Schuster Laboratory, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
⁵  Institut de Recherches Subatomiques UMR7500, CNRS-IN2P3 and Université Louis Pasteur, 67037 Strasbourg, France
⁶  Argonne National Laboratory, Argonne, IL 60439, USA
⁷  Instuut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Heverlee, Belgium
⁸  Petersburg Nuclear Physics Institute, Russian Academy of Sciences, Gatchina, 188350, Russia
⁹  Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russia
¹⁰  Department of Physics Frescati, Royal Institute of Technology, S-10405 Stockholm, Sweden
¹¹  Dipartimento di Scienze Fisiche, Università di Napoli Federico II and Istituto Nazionale di Fisica Nucleare, Italy

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(Received 21 March 2002 / Published online: 31 October 2002)

Abstract
Excited states in the nucleus, populated in the -decay of , have been studied at the mass separator OSIRIS. The activity was produced via fast neutron-induced fission of target. A main result was the discovery of a very low-lying first-excited state of , at 13 keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the region. On the basis of this comparison, the energy of the ( ) _7^- isomer is estimated to be about 250 keV, some 100 keV lower than previously reported.

PACS
23.40.-s - Beta decay; double beta decay; electron and muon capture.
23.20.Lv - Gamma transitions and level energies.
21.60.Cs - Shell model.

© Società Italiana di Fisica, Springer-Verlag 2002