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

The X(5) symmetry describes nuclei at the critical point of the shape phase transition from axially deformed rotor nuclei to spherical vibrators. Nd-150, Sm-152, and Gd-154 were the first nuclei where the predicted charateristics of the X(5) symmetry were observed. Later it was shown that also Os-176,Os-178,Os-180 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 Os-178. 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 W-176. Thus we performed a recoil distance Doppler shift (RDDS) measurement on W-176 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 Dy-169(O-16,4n)W-176 and a beam energy of 80MeV. We will present our experimental results and ;relate them to data on the neighboring nuclei Os-178 and Pt-182. 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.