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Two nucleon transfer reactions at low bombarding energies are an ideal tool to investigate nucleon-nucleon correlations. With heavy ions one has the possibility to transfer several nucleon pairs, involving both neutrons and protons at the same time. In this work we will study how pair correlations can be probed in heavy ion collisions , and how the strong Coulomb field influences the reaction dynamic.

Pair correlations have been investigated in heavy-ion collisions via studies of the transfers of different nucleon pairs. In particular, excitation functions of one- and two-neutron transfer channels have been measured for the closed shell 40Ca + 96Zr and superfluid 60Ni + 116Sn systems from the Coulomb barrier energy to energies far below. By using the unique performance of the magnetic spectrometer PRISMA, in terms of resolution and efficiency, measurements at very low bombarding energies have been performed. The experimental transfer probabilities have been compared with semiclassical microscopic calculations that incorporate nucleonnucleon correlations, together with known structure information of entrance and exit channels nuclei and reaction dynamics. These calculations well reproduce, in the whole energy range, one- and two-neutron transfer channels in shape and magnitude.

International audience; We studied multinucleon transfer reactions in the Au197+Te130 system at Elab=1.07 GeV by employing the PRISMA magnetic spectrometer coupled to a coincident detector. For each light fragment we constructed, in coincidence, the distribution in mass of the heavy partner of the reaction. With a Monte Carlo method, starting from the binary character of the reaction, we simulated the de-excitation process of the produced heavy fragments to be able to understand their final mass distribution. The total cross sections for pure neutron transfer channels have also been extracted and compared with calculations performed with the grazing code.

Charge state distributions of the Ra recoil ions produced in the 12C+Pb fusion-evaporation reactions have been obtained by measuring their yields as a function of the high voltage applied to an electrostatic deflector. Well-defined two-humped yield curves for evaporation residues (ERs) were observed. Such observations can be explained by the different sets of charge states inherent in Ra recoil ions. These charge sets correspond to the equilibrated and nonequilibrated components, as earlier observed for evaporation residues produced in different reactions. The main parameters of the distributions (mean charge values, widths, and relative intensities) for both components have been estimated using Monte Carlo simulations of the transmission of the Ra recoil ions through the deflector. For the equilibrated component the values of the mean charge and width are close to those given by different empirical systematics. For the nonequilibrated component these parameters have been obtained for the first time. The additional nonequilibrated ionization is presumably due to the formation of inner shell vacancies produced by the internal conversion of nuclear isomeric transitions of ERs. Nonequilibrated charge parameters obtained for Ra recoil ions are compared to similar available experimental data and some theoretical predictions.

We measured multinucleon transfer reactions in the 40Ar+208Pb system at an energy close to the Coulomb barrier, by employing the PRISMA magnetic spectrometer. We extracted differential and total cross sections of the different transfer channels, with a careful investigation of the total kinetic energy loss distributions. A comparison between different systems having the same 208Pb target and with projectiles going from neutron-poor to neutron-rich nuclei, i.e., 40Ca, 58Ni, and 40Ar, as well as between the data and GRAZING calculations have been carried out. The neutron-rich (stable) 40Ar beam allowed us to get access to the channels involving proton pick-up, whose behaviour in connection with the production of neutron-rich heavy partner has been outlined.

Background: Multinucleon transfer reactions (MNT) are a competitive tool to populate exotic neutron-rich nuclei in a wide region of nuclei, where other production methods have severe limitations or cannot be used at all. Purpose: Experimental information on the yields of MNT reactions in comparison with theoretical calculations are necessary to make predictions for the production of neutron-rich heavy nuclei. It is crucial to determine the fraction of MNT reaction products which are surviving neutron emission or fission at the high excitation energy after the nucleon exchange. Method: Multinucleon transfer reactions in 136Xe+238U have been measured in a high-resolution γ-ray/particle coincidence experiment. The large solid-angle magnetic spectrometer PRISMA coupled to the high-resolution Advanced Gamma Tracking Array (AGATA) has been employed. Beamlike reaction products after multinucleon transfer in the Xe region were identified and selected with the PRISMA spectrometer. Coincident particles were tagged by multichannel plate detectors placed at the grazing angle of the targetlike recoils inside the scattering chamber. Results: Mass yields have been extracted and compared with calculations based on the grazing model for MNT reactions. Kinematic coincidences between the binary reaction products, i.e., beamlike and targetlike nuclei, were exploited to obtain population yields for nuclei in the actinide region and compared to x-ray yields measured by AGATA. Conclusions: No sizable yield of actinide nuclei beyond Z=93 is found to perform nuclear structure investigations. In-beam γ-ray spectroscopy is feasible for few-neutron transfer channels in U and the −2p channel populating Th isotopes. Background: Multinucleon transfer reactions (MNT) are a competitive tool to populate exotic neutron-rich nuclei in a wide region of nuclei, where other production methods have severe limitations or cannot be used at all. Purpose: Experimental information on the yields of MNT reactions in comparison with theoretical calculations are necessary to make predictions for the production of neutron-rich heavy nuclei. It is crucial to determine the fraction of MNT reaction products which are surviving neutron emission or fission at the high excitation energy after the nucleon exchange. Method: Multinucleon transfer reactions in 136Xe+238U have been measured in a high-resolution γ-ray/particle coincidence experiment. The large solid-angle magnetic spectrometer PRISMA coupled to the high-resolution Advanced Gamma Tracking Array (AGATA) has been employed. Beamlike reaction products after multinucleon transfer in the Xe region were identified and selected with the PRISMA spectrometer. Coincident particles were tagged by multichannel plate detectors placed at the grazing angle of the targetlike recoils inside the scattering chamber. Results: Mass yields have been extracted and compared with calculations based on the grazing model for MNT reactions. Kinematic coincidences between the binary reaction products, i.e., beamlike and targetlike nuclei, were exploited to obtain population yields for nuclei in the actinide region and compared to x-ray yields measured by AGATA. Conclusions: No sizable yield of actinide nuclei beyond Z=93 is found to perform nuclear structure investigations. In-beam γ-ray spectroscopy is feasible for few-neutron transfer channels in U and the −2p channel populating Th isotopes.

International audience; The level structure of the neutron-rich 69Cu, 71Cu, and 73Cu isotopes has been investigated by means ofmultinucleon transfer reactions. The experiment was performed at Laboratori Nazionali di Legnaro using theAGATA Demonstrator array coupled to the PRISMA magnetic spectrometer. Lifetimes of excited states inCu nuclei were measured with the recoil-distance Doppler-shift method. The resulting electromagnetic matrixelements for transitions from excited states in 69,71,73Cu nuclei are used to assess the collective or single-particlecharacter of these states. The results are compared with predictions of large-scale shell-model calculations, givingfurther insight into the evolution of the proton pf shell as neutrons fill the 1g9/2 orbital.

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. Reakcije prijenosa nukleona na energijama blizu kulonske barijere važne su i u proučvanju strukture jezgara i mehanizma reakcije. Pokazalo se da su teškoionske reakcije odličan način proučavanja rezidualne interakcije u jezgrama, naročito dijelova odgovornih za vezanje i korelacije. Glavna tema ovog doktorskog rada je proučavanje svojstava nuklearne sile koja nisu uključena u opis pomoću srednjeg polja, posebno uloga korelacija između neutrona i protona. To se proučavalo mjerenjem reakcije prijenosa mnogo nukleona s magnetskim spektrometrom velikoga prostornoga kuta PRISMA i njegovim pomoćnim detektorima. Dobiveni su diferencijalni i ukupni udarni presjek, raspodjela gubitka kinetičke energije za sve produkte reakcije, te su uspoređeni s teorijskim predviđanjima modela GRAZING. Glavna ideja je potraga za eksperimentalnim potpisom prijenosa koreliranog para neutron-proton u području blizu Z = 20 i N = 20 zatvorenih ljusaka. Istodobnom usporedbom apsolutnog udarnog presjeka za sve kanale koje su pobuđeni prijenosom para nukleona, (±nn), (±pp) i (±np), te njihovom usporedbom s teorijskim predviđanjima, traženi su mogući efekti (np) korelacija. Rezultati su potvrđeni s rezultatima dobivenim na energijama ispod kulonske barijere, gdje se očekuju male energije pobuđenja produkata reakcije. Usporedba mjerenih rezultata s polu-klasičnim računima koji uključuju samo prijenos neovisnih čestica pokazuje da je (+1p+1n) kanal pojačan, što može ukazivati na moguć doprinos (np) korelacija. Analiza inkluzivnih podataka je nadopunjena dodatnom analizom γ-fragment koincidencija, kada je PRISMA korištena s CLARA γ detektorom. Ove koincidencije omogućuju proučavanje snage pobuđenja različitih stanja. 42K kanal, pobuđen putem prijenosa jednog protona i neutrona, pokazuje jako pobuđenje 7+ stanja. Taj rezultat se može shvatiti kao dodatna potvrda prisutnosti korelacije neutron-proton, jer se 7+ stanje može opisati kao stanje u kojem su neutron i proton u istoj f7/2 orbitali.

The 14N(p, γ)15O reaction is the slowest process of the CN cycle, and thus it is of high astrophysical interest since it regulates the total rate of energy and neutrinos production through the cycle. The 14N+p ground state capture is strongly influenced by a sub-threshold resonance corresponding to the 6.79 MeV state in 15O. The width of this resonance is a major source of uncertainty in the extrapolation of the reaction cross section in the Gamow energy window. Preliminary results of a new Doppler Shift Attenuation measurement of the lifetime of the 6.79 MeV state in 15O are discussed. The level of interest was populated via the 2H(14N, n)15O reaction in inverse kinematics at 32 MeV beam energy. The gamma-rays emitted in the decay of the 6.79 MeV level to the ground state were detected with the AGATA Demonstrator array of high-purity germanium detectors. The sensitivity of the shape of the peak in the gamma-ray energy spectrum to the level lifetime is investigated comparing the experimental peaks with detailed Monte Carlo simulations of the reaction mechanisms and the gamma-ray emission and detection. Nuclear levels in 15N (also populated in the 14N+2H reaction) for which the lifetimes are known in the literature provided a test of the analysis technique.