B. Melon

Lifetimes of odd-spin yrast states in {sup 182}Hg

Lifetimes of excited states in {sup 182}Hg were extracted from recoil-gated {gamma}-ray spectra and recoil-gated {gamma}{gamma}-coincidence matrices using the recoil distance Doppler-shift method. States were populated using the {sup 96}Mo({sup 88}Sr,2n){sup 182}Hg fusion-evaporation reaction. Measured lifetimes allowed transition probabilities, transition quadrupole moments, quadrupole deformation parameters, and transition dipole moments to be deduced for the band formed by the odd-spin yrast states. The experimental results confirm the low degree of octupole collectivity in this mass region.

Evolution of collectivity in {sup 180}Hg and {sup 182}Hg

Lifetimes of yrast states in {sup 180}Hg up to the 8{sup +} state and of the 9{sup -} state have been extracted from recoil-decay tagged {gamma}-ray spectra by using the recoil distance Doppler-shift method. In addition, lifetimes of yrast states up to the 10{sup +} state in {sup 182}Hg have been extracted from recoil-gated {gamma}{gamma}-coincidence spectra. The present study addresses the evolution of collectivity of two competing shapes in neutron-deficient Hg nuclei as a function of A and the configuration mixing at low spin.

Collectivity of {sup 196}Po at low spin

Absolute electromagnetic transition probabilities in Po196 have been measured using the recoil distance Doppler-shift technique. The lifetimes of the three lowest yrast states in Po196 were extracted from singles γ-ray spectra by using the recoil-decay tagging method. In addition, configuration mixing calculations of angular momentum projected mean-field states have been carried out for Po196. The present study sheds light on the onset of collectivity and mixing of competing structures in neutron-deficient Po nuclei.

Development of a new Recoil Distance Technique using Coulomb Excitation in Inverse Kinematics

We report on an experiment using Coulomb excitation in inverse kinematics in combination with the plunger technique for measuring lifetimes of excited states of the projectiles. Aside from the investigation of E(5) features in 128Xe, the aim was to explore the special features of such experiments which are also suited to be used with radioactive beams. The measurement was performed at the JYFL with the Koln coincidence plunger device and the JUROGAM spectrometer using a 128Xe beam impinging on a natFe target at a beam energy of 525 MeV. Recoils were detected by means of 32 solar cells placed at extreme forward angles. Particle‐gated γ‐singles and γγ‐coincidences were measured at different target‐degrader distances. Details of the experiment and first results are presented.

Plunger lifetime measurements after Coulomb excitation at intermediate beam energies

Absolute transition probabilities of the first 2{sup +} state in {sup 110,114}Pd were remeasured using the recoil distance Doppler shift technique following projectile Coulomb excitation at intermediate beam energies for the first time. The {sup 110}Pd experiment served to check the novel technique as well as the method used for the data analysis which is based on the examination of {gamma}-ray lineshapes. Whereas the measured B(E2) value for {sup 110}Pd agrees very well with the literature, the value obtained for {sup 114}Pd differs considerably. The data is also used to test a novel concept, called the valence proton symmetry, which allows one to extrapolate nuclear properties to very neutron rich nuclei.

Probing collectivity in the vicinity of neutron deficient Pb nuclei

A series of recoil distance Doppler‐shift lifetime measurements have been carried out to probe collectivity and configuration mixing of different shapes in the vicinity of neutron mid‐shell Pb nuclei. Lifetime measurements of 186Pb and 194Po, the first ever utilizing the recoil‐decay tagging method, probed the collectivity of coexisting prolate and oblate shapes in this region. Futher lifetime measurements of excited states in 180Hg, 182Hg and 196Po have been carried out.