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Séminaire présenté par Karolina Kolos, Institut de Physique Nucléaire, Orsay

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Study of 84Ga beta decay at the ALTO facility

Par : Karolina Kolos, Institut de Physique Nucléaire, Orsay
Date : mercredi 18 avril 2012 à 11h00
Lieu : IPHC, Salle de Réunion 2e étage du Bâtiment 27

Résumé :

A recent advance in the production and purification of radioactive ion beams have made a region of nuclei near the doubly magic 78Ni more accessible for the experimental studies. This region, with very neutron­rich 78Ni hypothetically considered as a doubly magic core, is interesting in terms of nuclear structures. There is an increasing interest in studying the evolution of the collectivity of neutron­rich nuclei beyond N = 50. Germanium isotopes are well known to undergo collective effects such as vibrations or gamma softness. It is particularly interesting to study 84Ge as it is the most exotic even­even (Z = 32, N = 52) nucleus beyond N = 50 presently accessible to experiment. The nature of the collectivity can be probed by measuring the excitation energies of the first
2+, 4+, 0+ states. This experimental information is important to guide
2+ the emerging shell­model effective interactions in this region and provide us the microscopic description of the origin of this collectivity.

We have studied beta­decay of a neutron rich 84Ga isotope at the ALTO facility in IPN Orsay (France). The fission fragments were produced with photo­fission reaction induced by 50 MeV electron beam in a thick UCx target. For the first time the maximum electron driver beam intensity at ALTO ­ 10µA ­ was used. The gallium atoms were selectively ionized with a newly developed laser ion source. With this ion source the ionization of the gallium was more than ten times higher compared to the surface ion source previously used by our group. The ions were separated with the PARRNe mass separator and implanted on a movable mylar tape. Two germanium detectors in close geometry were used for the detection of gamma­ rays and gamma­-gamma coincidence measurement, and a plastic 4 gamma for beta tagging.

The improved level scheme for 84Ge will be presented and compared with the shell model calculations performed with ANTOINE code using "ni78­jj4b" interaction, which is the modified version of the residual interaction developed by K. Sieja with the 78Ni core.

Personne à contacter : Kamila SIEJA