"Lifetime measurements of low-lying states in neutron-rich Zn isotopes by the plunger technique"
Megumi Niikura, IPN Orsay
(id #84)
Seminar: YesPoster: No
Invited talk: No
One of the most critical ingredients in determining the disappearance or appearance of magicity in nuclei far from stability is the evolution of single-particle energies with increasing neutron or proton numbers when moving away from the valley of stability. The three known cases of disappearance of shell effects at N=8, 20 and 28 in neutron-rich nuclei are understood as due to the effect of the tensor part of the nucleon-nucleon interaction. The tensor force is held responsible for the strong attraction between a proton and a neutron in spin-flip partner orbits. A recent generalization of such mechanism foresees a similar behavior also for orbitals with non-identical
orbital angular momenta. It is expected that orbitals with anti-parallel angular momenta attract each other and orbitals with parallel angular momenta repulse each other.
In this context neutron-rich nuclei in the vicinity of 78Ni are particularly interesting since they allow to search for anomalies when compared with shell-model predictions. It is predicted, for example, that the Z=28 gap for protons in the pf-shell becomes smaller when moving from N=40 to 50 as a consequence of the attraction between the proton f5/2 and neutron g9/2 orbits and the repulsion between the proton f7/2 and the neutron g9/2 states. The same argument would also predict a weakening of the N=50 shell gap when depleting the proton f5/2 state upon approaching the 78Ni nucleus, due to the diminished attraction between the neutron f9/2 and the proton f5/2 orbits and the reduced repulsion between the neutron g9/2 and the proton f5/2 states.
In order to investigate the shell evolution in the vicinity of 78Ni we have performed lifetime measurements for low-lying states in 72-74Zn by the differential plunger technique. A cocktail beam of 73,74Zn was produced by the projectile-fragmentation reaction of 76Ge on a 9Be target and
separated by the first half of the LISE spectrometer at GANIL. The secondary beam with the energy of 34 MeV/nucleon was bombarding on a secondary CD2 target to induce inelastic and transfer reactions, and outgoing particles were selected and identified by the second half of LISE. Gamma rays emitted from the reaction products were detected by 8 EXOGAM detectors, which were surrounding secondary target at 45 and 135 degrees relative to the beam direction. The differential plunger technique with 9Be degrader was applied to measure lifetimes of excited states.
The first results of the lifetime measurement in low-lying states in 72,73,74Zn will be reported together with the comparison to results from Coulomb excitation experiments at REX-ISOLDE and GANIL. A picture of the low-energy structure in these isotopes towards the middle of the νg9/2 orbital will be given via: i) identification of the levels populated with inelastic scattering reaction and ii) determination, in a model-independent way, of the transition probabilities of those levels
towards the ground state.
orbital angular momenta. It is expected that orbitals with anti-parallel angular momenta attract each other and orbitals with parallel angular momenta repulse each other.
In this context neutron-rich nuclei in the vicinity of 78Ni are particularly interesting since they allow to search for anomalies when compared with shell-model predictions. It is predicted, for example, that the Z=28 gap for protons in the pf-shell becomes smaller when moving from N=40 to 50 as a consequence of the attraction between the proton f5/2 and neutron g9/2 orbits and the repulsion between the proton f7/2 and the neutron g9/2 states. The same argument would also predict a weakening of the N=50 shell gap when depleting the proton f5/2 state upon approaching the 78Ni nucleus, due to the diminished attraction between the neutron f9/2 and the proton f5/2 orbits and the reduced repulsion between the neutron g9/2 and the proton f5/2 states.
In order to investigate the shell evolution in the vicinity of 78Ni we have performed lifetime measurements for low-lying states in 72-74Zn by the differential plunger technique. A cocktail beam of 73,74Zn was produced by the projectile-fragmentation reaction of 76Ge on a 9Be target and
separated by the first half of the LISE spectrometer at GANIL. The secondary beam with the energy of 34 MeV/nucleon was bombarding on a secondary CD2 target to induce inelastic and transfer reactions, and outgoing particles were selected and identified by the second half of LISE. Gamma rays emitted from the reaction products were detected by 8 EXOGAM detectors, which were surrounding secondary target at 45 and 135 degrees relative to the beam direction. The differential plunger technique with 9Be degrader was applied to measure lifetimes of excited states.
The first results of the lifetime measurement in low-lying states in 72,73,74Zn will be reported together with the comparison to results from Coulomb excitation experiments at REX-ISOLDE and GANIL. A picture of the low-energy structure in these isotopes towards the middle of the νg9/2 orbital will be given via: i) identification of the levels populated with inelastic scattering reaction and ii) determination, in a model-independent way, of the transition probabilities of those levels
towards the ground state.
