Eur. Phys. J. A (2009) 39: 49-51
https://doi.org/10.1140/epja/i2008-10692-4

Regular Article - Experimental Physics

Revised spin-parity assignment and a new interpretation of the high-spin isomer in ¹⁵¹Er

¹ Department of Physics, Osaka University, Machikaneyama-machi 1-1, Osaka 560-0043, Toyonaka, Japan
² RIKEN, Hirosawa 2-1, Saitama 351-0198, Wako, Japan
³ Center for Nuclear Study, University of Tokyo, Hirosawa 2-1, Saitama 351-0198, Wako, Japan
⁴ Cyclotron and Radio-isotope Center, Tohoku University, Aoba 6-3, Sendai, 980-8578, Aobaku, Japan
⁵ Department of Physics, Tohoku University, Aoba 6-3, Sendai, 980-8578, Aobaku, Japan

^* e-mail: odahara@phys.sci.osaka-u.ac.jp

Received: 20 July 2008
Revised: 7 October 2008
Published online: 15 December 2008

Abstract

The high-spin isomer in ¹⁵¹Er ( E _x = 10.3 MeV, T _1/2 = 420 ns) has been studied by the ¹¹⁶Sn ( ⁴⁰Ar , 5n) ¹⁵¹Er reaction at 197MeV. From the coincidence relations, a new transition with an energy of 1514keV was found. This finding requires the revision of the spin-parity assignment from previous 67/2^- to 61/2⁺ or 65/2^- . The 61/2⁺ assignment is the one which was predicted by the deformed independent particle model as an isomer with a large oblate deformation ( = - 0.17) of the configuration. The isomerism may be attributed to the sudden shape change of the isomer from the nearly spherical shape of the lower-spin yrast states to the oblate shape.