engleski

Study of heavy-ion reactions with large solid angle magnetic spectrometers

Nucleon transfer reactions at energies close to the Coulomb barrier always played an important role in nuclear structure and reaction dynamics studies. It has been shown that heavy-ion reactions are an ideal tool for the study of the residual interaction in nuclei, in particular the components responsible for the couplings and correlations. The main subject of the present thesis is the study of the properties of the nuclear force which are not accounted for by the mean field description, especially the role played by neutron-proton correlations. This has been addressed by measurements of multinucleon transfer reactions performed with the new generation magnetic spectrometer PRISMA and its ancillary detectors. The experimental differential and total cross sections and total kinetic energy loss distributions for the final reaction products have been extracted and compared with the predictions of the GRAZING model for heavy-ion transfer reactions, based on semi-classical theory. The main objective was to search for an experimental signature of transfer of correlated neutron-proton pairs in the region near the Z =20 and N =20 shell closures. Through the simultaneous study of the absolute cross sections for all channels populated via transfer of nucleon pairs (±nn), (±pp) and (±np), and their comparison with the theoretical predictions, we explored the possible effect of (np) correlation. The findings have been also corroborated with results obtained at energies below the Coulomb barrier, where the excitation energies of the final reaction products are expected to be small. The comparison of the experimental results with the semi-classical calculations that include only the transfer of independent particles shows that the experimental cross section of (+1p+1n) channel is enhanced, indicating the possibility of a presence of a (np) pair degree of freedom. The analysis of these inclusive data was corroborated by a complementary analysis of γ-particle coincidences, where PRISMA has been used in coupled operation with the CLARA γ array. From the analysis of these coincidences, the population strength of excited states has been extracted for different transfer channels. In particular, for 42K, reached via the (+1p+1n) channel, a strong population of the 7+ state has been evidenced. Since this can happen when a neutron and a proton occupy the same f7/2 orbital, the finding may give a further support to the presence of a neutron-proton correlation.

multinucleon transfer reactions ; magnetic spectrometers ; nucleon-nucleon correlations ; differential and total cross sections

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