[in2p3-00022465] On-line γ spectroscopy of $^{32}$Mg produced by projectile fragmentation and study of $^{36}$Ca and $^{35}$Ca radioactivity

The thesis is devoted to study of nuclei far from stability, produced with the GANIL facility by projectile fragmentation at intermediate energies. It concerns two parts. In the first part an experiment in which the 35-36Ca proton-rich nuclei were produced at the LISE3 spectrometer is presented. Two new excited levels have been deduced from the observed β-delayed proton emission of 36Ca. The measured Gamow-Teller strengths are in good agreement with shell model calculation if a standard quenching factor of 0.77 for the sd shell is used. In the second part of the thesis a novel experimental method has been used. This method is based on the production of very neutron-rich nuclei in excited states and on the detection of their in-beam γ-decay. Thanks to the high efficiency and granularity of the γ-detectors and the high selectivity of the SPEG spectrometer, an unambiguous assignment of the observed γ-rays to the exotic nuclei of interest was achieved. A new transition at 1440±3 keV has been observed for the 32Mg in coincidence with the well-known transition from the 2+ to the 0+ level at 885 keV. An analysis of the multipolarity of this transition based on the γ-ray angular distribution and its population is presented. Experimental results are compared with shell model calculations. A population of the excited levels in the fragmentation-like reactions was studied by means of the γ-ray multiplicity and energy measurements. A strong correlation between the sum. of the γ-ray energies and the one-neutron separation energy was observed. That could mean that the nuclei are populated above the one-neutron separation energy. It was also shown that the population of the excited states depends on the fragment velocity.



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