Eur. Phys. J. A 17, 167-171 (2003)
DOI: 10.1140/epja/i2003-10002-x

In-beam -ray spectroscopy of : First observation of a low-lying prolate band in Po isotopes

K. Van de Vel¹, A.N. Andreyev^{1, 2}, R.D. Page², H. Kettunen³, P.T. Greenlees³, P. Jones³, R. Julin³, S. Juutinen³, H. Kankaanpää³, A. Keenan³, P. Kuusiniemi³, M. Leino³, M. Muikku³, P. Nieminen³, P. Rahkila³, J. Uusitalo³, K. Eskola⁴, A. Hürstel⁵, M. Huyse¹, Y. Le Coz⁵, M.B. Smith⁶, P. Van Duppen¹ and R. Wyss<sup>7

1</sup>  Instituut voor Kern- en Stralingsfysica, University of Leuven, Belgium
²  Oliver Lodge Laboratory, Department of Physics, University of Liverpool, UK
³  Department of Physics, University of Jyväskylä, Finland
⁴  Department of Physics, University of Helsinki, Finland
⁵  DAPNIA/SPhN, CEA Saclay, France
⁶  Department of Physics and Astronomy, Rutgers University, USA
⁷  Department of Physics, Royal Institute of Technology, Stockholm, Sweden

karen.vandevel@fys.kuleuven.ac.be

(Received: 10 January 2003 / Revised version: 19 February 2003 / Published online: 7 May 2003)

Abstract
Gamma rays from excited states of ¹⁹⁰Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin onwards resembles the prolate rotational bands known in the isotones ¹⁸⁸Pb and ¹⁸⁶Hg. This indicates that in ¹⁹⁰Po the prolate configuration becomes yrast above . The experimental results are interpreted in a two-band mixing calculation and are in agreement with -decay data and potential energy surface calculations.

PACS
23.20.Lv - Gamma transitions and level energies.
25.70.-z - Low and intermediate energy heavy-ion reactions.
27.80.+w - .
21.60.Ev - Collective models.

© Società Italiana di Fisica, Springer-Verlag 2003