Lifetime measurements of excited states in 163W

The evolution of nuclear structure in the neutron-deficient W isotopes has revealed that the transitional nucleus 163W (N=89) occupies an intriguing position in the chain of W isotopes. The neutron Fermi surface in the neutron-deficient W isotopes lies close to f7/2, h9/2 and i13/2 subshell orbitals. Previous studies have indicated that the first backbend in 164W is due to the rotational alignment of a pair of i13/2 neutrons, whereas in 162W a pair of h9/2 neutrons were found to be the cause of the first backbend. This implies that configurations involving h9/2 and i13/2 orbitals should be at similar excitation energies in 163W and hence compete to form the yrast states.

Previous experiments have already established excited states in 163W, including yrast states built on the vi13/2 orbital and bands built on the vh9/2 and vf7/2 configurations. In order to measure the mean lifetimes of excited states in 163W, recoil-tagged y-y coincidence RDDS measurements have been performed using the DPUNS plunger device in conjunction with the RITU gas-filled separator and the JUROGAM II and GREAT spectrometers. Lifetimes and nuclear deformations of low lying states in the yrast band will be extracted from the data and analysed in the context of measurements of the neighbouring isotopes.