Eur. Phys. J. A (2005) 26: 19-24
https://doi.org/10.1140/epja/i2005-10132-1

Original Article

Suppression of band crossing in the neutron-rich nuclei ^{172, 173}Yb due to the absence of a static pair field

¹ Institut für Kernphysik, Forschungszentrum Jülich, D-52425, Jülich, Germany
² Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, BG-1784, Sofia, Bulgaria
³ Sezione di Padova, Dipartimento di Fisica dell'Università and INFN, I-35131, Padova, Italy
⁴ Laboratori Nazionali di Legnaro, INFN, I-35020, Legnaro, Italy
⁵ A.F. Ioffe Physical Technical Institute RAS, RU-194021, St. Petersburg, Russia
⁶ Institute of Experimental Physics, University of Warsaw, PL-00-681, Warszawa, Poland
⁷ Department of Physics, University of Notre Dame, Notre Dame, IN, USA
⁸ Institut für Kern- und Hadronenphysik, Forschungszentrum Rossendorf, D-01314, Rossendorf, Germany

^* e-mail: r.lieder@fz-juelich.de

Received: 12 April 2005
Accepted: 3 August 2005
Published online: 20 September 2005

Abstract

High-spin states in the neutron-rich nuclei ^172,173Yb have been populated in a ¹⁷⁰Er(⁷Li,(p,d,t)xn) incomplete-fusion reaction and the emitted γ-radiation was detected with the GASP array. The signature partners of the 7/2⁺[633] rotational band of the odd-N ¹⁷³Yb isotope have been newly established and were observed up to spin values of (45/2⁺) and (43/2⁺), respectively. The ground-state band of the even-even nucleus ¹⁷²Yb has been observed up to a spin value of (22⁺). No band crossings were found in these bands. To explain this observation, it is proposed that the static pair field is absent, considering that the neutron odd-even mass differences reach for these nuclei very small values and that the band crossing is absent in cranked shell modell calculations without pairing. The results indicate, however, that strong dynamic correlations are still present.