Eur. Phys. J. A (2003) 20: 173-178
https://doi.org/10.1140/epja/i2002-10347-6

Shape changes and test of the critical-point symmetry X(5) in N = 90 nuclei

¹ Institut für Kernphysik der Universität zu Köln, Köln, Germany
² Institute for Nuclear Research and Nuclear Energy Sofia, Sofia, Bulgaria
³ W.N.S.L., Yale University, CT 06520, New Haven, USA
⁴ Dipartimento di Fisica dell’ Universitá and INFN Sezione Padova, Padova, Italy
⁵ INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy
⁶ Physik-Department E12, TU München, Garching, Germany

^* e-mail: Alfred.Dewald@ikp.Uni-Koeln.de

Abstract

Reliable and precise lifetimes of excited states in ¹⁵⁴ Gd and ¹⁵⁶ Dy were measured using the recoil distance Doppler shift (RDDS) technique. Excited states of ¹⁵⁴ Gd were populated via Coulomb excitation with a ³² S beam at 110 MeV delivered by the FN tandem accelerator at the University of Cologne. For ¹⁵⁶ Dy a coincidence plunger experiment was performed at the Laboratori Nazionali di Legnaro with the GASP spectrometer and the Cologne coincidence plunger apparatus using the reaction ¹²⁴ Sn(³⁶ S,4n)¹⁵⁶ Dy at a beam energy of 155 MeV. Shape changes previously suggested to appear in the ground-state band (gsb) of ¹⁵⁶ Dy and in the s-band above the first band crossing were not supported by the transition probabilities determined in this work. The measured transition probabilities of ¹⁵⁶ Dy and ¹⁵⁴ Gd as well as the corresponding energy spectra are compared with the predictions of the recently proposed X(5) model and in the case of ¹⁵⁶ Dy also with an IBA fit.