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Beta decay studies close to the doubly-magic nucleus 78Ni

Thanks to the advances in the production of neutron-rich nuclei in the last two decades, we are now able to explore nuclei very far from the stability. The region of the nuclear landscape in the vicinity of 78Ni, which is expected to be a doubly-magic nucleus, is still unexplored and is very interesting in terms of nuclear structure, since it allows to test the validity of the shell-model at large N/Z ratios. With this in mind, we have studied the β-decay of the neutron rich 84Ga isotope at the ALTO facility in IPN Orsay (France). The 84Ga nucleus was produced via a photo-fission reaction induced by a 50 MeV electron beam of 10 µA of intensity on a thick UCx target. The gallium atoms were then selectively ionized with a newly developed laser ion source, 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 the ɣ-rays emitted after the β -decay, and a plastic 4πβ scintillator for beta tagging. The work I was involved primarily is the first step of a complex data analysis, consisting of the study of the time distribution of all the measured ɣ-transitions, in order to attribute each of them to the correct nucleus. The final results of the experiment are the improved level schemes of the neutron-rich 83;84Ge and 84As isotopes. Shell-model calculations, performed by using the new effective ni78 - jj4b interaction, reproduce quite well the experimental results.

Mostra/Nascondi contenuto.
Chapter 1 Nuclear structure far from stability towards 78 Ni In the present thesis I shall describe an experiment performed last year with the PARRNe-ALTO facility in Orsay, whose aim is the study of the exotic neutron-rich nuclei in the vicinity of 78 Ni. This is part of a series of experiments on the nuclei of this poorly explored region done in Orsay and in other laboratories as well (Cern, Oak Ridge). The 78 Ni nucleus, whose structure is still unknown, has 28 protons and 50 neutrons, and therefore in the framework given by the shell model it is expected to be one of the few doubly-magic nuclei (see fig. 1.1). Those “special” nuclei are used as cores for shell-model calculations, dramatically truncating the model space, thus rendering feasible shell-model calculations in heavy nuclei. The 78 Ni nucleus is also one of the waiting-points in the astrophysical r-process; to test the rigidity of its associated gaps is of special interest also for this reason. However, the study of 78 Ni nucleus is not yet feasible and it requires the next generation of radioactive beam facilities. One can anyway derive some informations on the properties of the Z = 28 and N = 50 shell gaps by studying the more accessible close-by nuclei. As I shall show in detail in the present thesis, we have studied the -decay of the neutron rich 84 Ga isotope and of its daughters. The nucleus of interest, as many others, was produced via a photo-fission reaction induced by an 50 MeV electron beam of 10 A on a thick UCx target. The gallium atoms were selec- tively ionized with a newly developed laser ion source. 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 -rays and - coincidence measurement, and a plastic 4 for beta tagging. The final results of this experiment are the improved level schemes of the neutron-rich 83;84 Ge and 84 As isotopes. 1

Tesi di Laurea Magistrale

Facoltà: Scienze Matematiche, Fisiche e Naturali

Autore: Giacomo Germogli Contatta »

Composta da 88 pagine.

 

Questa tesi ha raggiunto 34 click dal 21/12/2012.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.