Measurement of absolute E2 transition strengths in [sup 176]W: Signatures for a rapid shape change

Abstract

The X(5) symmetry describes nuclei at the critical point of the shape phase transition from axially deformed rotor nuclei to spherical vibrators. 150 Nd, 152 Sm, and 154 Gd were the first nuclei where the predicted charateristics of the X(5) symmetry were observed. Later it was shown that also 176,178,180 Os can be successfully described with the X(5) symmetry.In the close vicinity of shape phase transitions one expects strongly changing nuclear shapes. In the X(5) region around A=150 this was observed for nuclei with different neutron numbers, whereas in the X(5) region around A=180 this is to be expected for different proton numbers. The aim of the work presented here is the confirmation of a rapid shape change for nuclei close to 178 Os. Besides the knowledge on the level scheme of the nuclei of interest, especially absolute E2 transition strengths are crucial for the interpretation of nuclear structure. Prolate deformation is expected for 176 W. Thus we performed a recoil distance Doppler shift (RDDS) measurement on 176 W to measure E2 transition strengths from level lifetimes. The experiment was performed at the Cologne FN TANDEM accelerator with the Cologne coincidence plunger with the reaction 169 Dy( 16 O,4n) 176 W and a beam energy of 80 MeV. We will present our experimental results and relate them to data on the neighboring nuclei 178 Os and 182 Pt. The results will be discussed in the framework of nuclear shape transitions in this mass region and compared to calculations with both the Interacting Boson Model (IBM) and the GCM.