Measurements of projectile fragments from 70 Zn (15 MeV/nucleon) + 64 Ni collisions with the MAGNEX spectrometer at INFN-LNS

The present work is focused on our efforts to produce and identify neutron-richrare isotopes from peripheral reactions below the Fermi energy. High-quality experimental data were obtained from a recent experiment with the MAGNEX spectrometer at INFN-LNS in Catania, Italy. The main goal of this effort is to describe the adopted identification techniques used to analyze the data from the reaction 70 Zn (15 MeV/nucleon) + 64 Ni. The particle identification procedure is based on a novel approach that involves the reconstruction of both the atomic number Z and the ionic charge q of the ions, followed by the identification of themass. Our method was successfully applied to identify neutron-rich ejectiles from multinucleon transfer in the above reaction 70 Zn + 64 Ni at 15 MeV/nucleon. The analysis of the data is ongoing. We expect to obtain the angular and momentum distributions of the fragments, along with their production cross sections. These data, along with comparisons with theoretical models are expected to contribute to a better understanding of the complex reaction mechanisms of multinucleon transfer that dominate this energy regime

Recent results on heavy-ion induced reactions of interest for neutrinoless double beta decay at INFN-LNS

Abstract. The possibility to use a special class of heavy-ion induced direct reactions, such as double charge exchange reactions, is discussed in view of their application to extract information that may be helpful to determinate the nuclear matrix elements entering in the expression of neutrinoless double beta decay halflife. The methodology of the experimental campaign presently running at INFN - Laboratori Nazionali del Sud is reported and the experimental challenges characterizing such activity are describe

A multi-channel approach to the study of the 18O+48Ti reaction within the NUMEN project

The study of the multi-nucleon transfer as competitive processes to the double charge exchange channel has a prominent position among the goals of the NUMEN project. Understanding the degree of competition between successive nucleon transfer and double charge exchange reactions is imperative for the description of the direct-meson exchange mechanism. Moreover, the study of these competing processes under the same experimental conditions provides the appropriate constraints in the experimental systematics that are particularly useful for the theoretical description of the reaction mechanism. To this extent, one- and two-nucleon transfer reactions in the 18O+48Ti collision at 275 MeV were measured for the first time, under the NUMEN and NURE experimental campaigns. Differential cross-section angular distribution measurements for the reaction ejectiles were performed by using the MAGNEX large acceptance magnetic spectrometer at INFN-LNS in Catania. Recent results for the one-nucleon and two-proton transfer reactions will be presented and discussed

Elastic scattering and reaction mechanisms for the system 7Be+28Si at near barrier energies

The present work refers to the study of elastic scattering and reaction products for the system 7Be + 28Si at near barrier energies, namely 13.2, 17.2, 19.8 and 22.0 MeV (E/VC.b.=1.14, 1.48, 1.71, 1.90). The goal of this work is to probe the energy dependence of the optical potential as well as the interplay between direct and compound nucleus mechanisms. The experiment was visualized at the EXOTIC beam line of the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro (INFN-LNL) in Italy. The various ejectiles were collected by six ΔE-E telescopes of the detector array of the EXOTIC facility, EXPADES, placed at symmetrical position to balance any beam divergence and to improve the statistics of the measurement. The elastic scattering data were analyzed into the optical model framework, following the same method as adopted previously for 6,7Li + 28Si. Comparisons between 7Be-present data and 6,7Li-previous data on the same target showed that, that both mirror nuclei, 7Li and 7Be present the same energy dependence of the optical potential. The behavior of imaginary part of the optical potential is compatible with the standard threshold anomaly, while the real part cannot be definitely interpreted into dispersion relations framework, due to the limited data points around Coulomb barrier. The reaction data were analyzed in both statistical model and Distorted Wave Born Approximation frameworks (DWBA) in order to disentangle the degree of competition between direct and compound channels. The energy evolution of the ratio of direct to total reaction cross section was mapped in comparison with similar data for 6Li and 7Li projectiles on a 28Si target, indicating larger transfer contributions for 7Be and 7Li than in the 6Li case. Fusion cross sections for the system under study were deduced and were found to be compatible with systematic as well as with the Universal Fusion Function (UFF). Moreover, ratios of fusion functions for 6Li to those for 7Li and 7Be were formed, indicating a hindrance of fusion for 7Li and 7Be with respect to those of 6Li below the barrier rather than an enhancement. This hindrance was also observed before for 7Li on various targets and together with the results obtained from our optical model analysis present a strong evidence for the similarity of 7Be with its mirror nucleus 7Li and not the 6Li one.Η παρούσα διδακτορική διατριβή αφορά τη μελέτη της ελαστικής σκέδασης και των μηχανισμών αντιδράσεων για το σύστημα 7Be + 28Si σε ενέργειες κοντά στο φράγμα Coulomb και συγκεκριμένα στα 13.2, 17.2, 19.8 and 22.0 MeV (E/VC.b.=1.14, 1.48, 1.71, 1.90). Στόχος της παρούσας μελέτης είναι ο προσδιορισμός της ενεργειακής εξάρτησης του οπτικού δυναμικού καθώς και ο προσδιορισμός της συνεισφοράς των άμεσων αντιδράσεων και των αντιδράσεων σύνθετου πυρήνα στην αντίδραση 7Be + 28Si. Το πειραματικό μέρος της μελέτης αυτής πραγματοποιήθηκε στην γραμμή EXOTIC του Εθνικού Εργαστηρίου του Legnaro (INFN-LNL) της Ιταλίας. Τα διάφορα προϊόντα της αντίδρασης 7Be + 28Si ανιχνεύτηκαν χρησιμοποιώντας έξι ΔΕ-Ε τηλεσκόπια από την ανιχνευτική διάταξη EXPADES. Τα τηλεσκόπια είχαν τοποθετηθεί στο θάλαμο σκέδασης σε συμμετρικές θέσεις γύρω από το στόχο για τον έλεγχο της συμμετρίας της δέσμης.Η ανάλυση των γωνιακών κατανομών της ελαστικής σκέδασης έγινε στα πλαίσια του Οπτικού Μοντέλου, ακολουθώντας την ίδια τεχνική όπως είχε εφαρμοστεί για τα συστήματα 6,7Li + 28Si. Από τη σύγκριση των δεδομένων για το σύστημα 7Be + 28Si με τα αντίστοιχα δεδομένα του συστήματος 7Li + 28Si, συμπεραίνουμε ότι ο πυρήνας 7Be συμπεριφέρεται όπως ο κατοπτρικός του πυρήνας 7Li και όχι όπως ο πυρήνας του 6Li. Το φανταστικό μέρος του οπτικού δυναμικού όπως προσδιορίστηκε από την ανάλυση των δεδομένων της ελαστικής σκέδασης, παρουσιάζει μια πτωτική τάση καθώς προσεγγίζουμε το φράγμα Coulomb με κατεύθυνση από τις μεγαλύτερες προς τις μικρότερες ενέργειες, μια συμπεριφορά συμβατή με την τυπική ανωμαλία κατωφλίου. Όσον αφορά το πραγματικό μέρος του οπτικού δυναμικού, δεν μπορούμε να πούμε με βεβαιότητα ότι συνδέεται με το αντίστοιχο φανταστικό μέρος μέσω των σχέσεων διασποράς καθώς στην περιοχή γύρω από το φράγμα Coulomb, όπου με βάση τις σχέσεις διασποράς αναμένεται μια αύξηση στο μέτρο του πραγματικού δυναμικού, διαθέτουμε μόλις ένα πειραματικό σημείο.Όσον αφορά τους μηχανισμούς αντιδράσεων, η ανάλυση των σχετικών δεδομένων έγινε στα πλαίσια του στατιστικού μοντέλου για την αποδιέγερση του σύνθετου πυρήνα καθώς στο πλαίσιο της Προσέγγισης Born παραμορφωμένου Κύματος (DWBA), προκειμένου να εκτιμήσουμε το ποσοστό συνεισφοράς των άμεσων αντιδράσεων και των αντιδράσεων σύνθετου πυρήνα στην αντίδραση 7Be + 28Si. Εν συνεχεία, υπολογίστηκε ο λόγος της ενεργού διατομής των άμεσων αντιδράσεων ως προς την ολική ενεργό διατομή της αντίδρασης. Η ενεργειακή εξάρτηση του λόγου για το υπό μελέτη σύστημα συγκρίθηκε με την αντίστοιχη ενεργειακή εξάρτηση του λόγου για τους πυρήνες 6Li και 7Li στον ίδιο στόχο όπου παρατηρείται μεγαλύτερη συνεισφορά, από ευθείς αντιδράσεις στην περίπτωση των πυρήνων 7Be και 7Li σε σύγκριση με τον πυρήνα του 6Li. Επίσης, υπολογίστηκαν οι ενεργές διατομές σύντηξης για το υπό μελέτη σύστημα οι οποίες βρέθηκαν σε εξαιρετική συμφωνία με παρόμοια δεδομένα που αφορούν αλλά ασθενικά δέσμια βλήματα καθώς και με την Καθολική Καμπύλη Σύντηξης (UFF). Επιπλέον, προσδιορίστηκαν οι λόγοι των καμπύλων σύντηξης του 6Li ως προς εκείνες για το 7Li και το 7Be όπου παρατηρήθηκε μια ελάττωση της ενεργού διατομής σύντηξης για τους πυρήνες 7Li και το 7Be ως προς τις αντίστοιχες τιμές για το 6Li στην περιοχή του φράγματος Coulomb και παρακάτω. Η ίδια ελάττωση είχε παρατηρηθεί και σε προηγούμενες μετρήσεις για τον πυρήνα του 7Li με διαφορετικούς στόχους. Η συστηματική αυτή συμπεριφορά του λόγου των καμπύλων σύντηξης σε συνδυασμό με τα αποτελέσματα της ενεργειακής εξάρτησης του οπτικού δυναμικού, αποτελούν μια ισχυρή απόδειξη ότι ο πυρήνας 7Be συμπεριφέρεται όπως ο κατοπτρικός του πυρήνας 7Li και όχι όπως ο πυρήνας του 6Li

Upgrade of the MAGNEX spectrometer toward the high-intensity phase of NUMEN

The NUMEN experimental activity with accelerated beams is performed at INFN–Laboratori Nazionali del Sud (LNS) in Catania using the Superconducting Cyclotron and the MAGNEX magnetic spectrometer. The scientific motivation of NUMEN is to extract experiment-driven information on the nuclear matrix elements entering in the expression of the 0νββ decay half-life. The reaction cross sections involved, especially for the double charge exchange process, are very low, thus limiting the present exploration to a few selected isotopes of interest in the context of typically low-yield experimental runs. In order to make feasible a systematic study of all the candidate nuclei, a major upgrade of the LNS facility is foreseen to increase the experimental yield by more than two orders of magnitude. To this purpose, frontier technologies are being developed for the accelerator and the detection systems. An updated description of the choices derived from the recent R&D activity on the target system and MAGNEX focal plane detector is given

The NUMEN Project: An Update of the Facility Toward the Future Experimental Campaigns

International audienceThe goal of NUMEN project is to access experimentally driven information on Nuclear Matrix Elements (NME) involved in the neutrinoless double beta decay (0νββ) by accurate measurements of the cross sections of heavy-ion induced double charge-exchange reactions. In particular, the (18O, 18Ne) and (20Ne, 20O) reactions are adopted as tools for β+β+ and β-β- decays, respectively. The experiments are performed at INFN - Laboratory Nazionali del Sud (LNS) in Catania using the Superconducting Cyclotron to accelerate the beams and the MAGNEX magnetic spectrometer to detect the reaction products. The measured cross sections are very low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. In order to make feasible a systematic study of all the candidate nuclei, a major upgrade of the LNS facility is foreseen to increase the experimental yield by more than two orders of magnitude. To this purpose, frontier technologies are being developed for both the accelerator and the detection systems. An update description of the NUMEN project is presented here, focusing on recent achievements from the R&D activity

Initial State Interaction for the 20^{20}Ne + 130^{130}Te and 18^{18}O + 116^{116}Sn Systems at 15.3 AMeV from Elastic and Inelastic Scattering Measurements

International audienceDouble charge exchange (DCE) reactions could provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To achieve this goal, a detailed description of the reaction mechanism is mandatory. This requires the full characterization of the initial and final-state interactions, which are poorly known for many of the projectile-target systems involved in future DCE studies. Among these, we intend to study the 20Ne + 130Te and 18O + 116Sn systems at 15.3 AMeV, which are particularly relevant due to their connection with the 130Te→130Xe and 116Cd→116Sn double-β decays. We measure the elastic and inelastic scattering cross-section angular distributions and compare them with theoretical calculations performed in the optical model, one-step distorted wave Born approximation, and coupled-channel approaches using the São Paulo double-folding optical potential. A good description of the experimental data in the whole explored range of transferred momenta is obtained provided that couplings with the 21+ states of the projectile and target are explicitly included within the coupled-channel approach. These results are relevant also in the analysis of other quasi-elastic reaction channels in these systems, in which the same couplings should be included

The NUMEN Heavy Ion Multidetector for a Complementary Approach to the Neutrinoless Double Beta Decay

International audienceNeutrinos are so far the most elusive known particles, and in the last decades many sophisticated experiments have been set up in order to clarify several questions about their intrinsic nature, in particular their masses, mass hierarchy, intrinsic nature of Majorana or Dirac particles. Evidence of the Neutrinoless Double-Beta Decay (NDBD) would prove that neutrinos are Majorana particles, thus improving the understanding of the universe itself. Besides the search for several large underground experiments for the direct experimental detection of NDBD, the NUMEN experiment proposes the investigation of a nuclear mechanism strongly linked to this decay: the Double Charge Exchange reactions (DCE). As such reactions share with the NDBD the same initial and final nuclear states, they could shed light on the determination of the Nuclear Matrix Elements (NMEs), which play a relevant role in the decay. The physics of DCE is described elsewhere in this issue, while the focus of this paper will be on the challenging experimental apparatus currently under construction in order to fulfil the requirements of the NUMEN experiment. The overall structure of the technological improvement to the cyclotron, along with the newly developed detection systems required for tracking and identifying the reaction products and their final excitation level are described

Recent experimental activity on heavy-ion induced reactions within the NUMEN project

The possibility to use a special class of heavy-ion induced direct reactions, such as double charge exchange reactions, is discussed in view of their application to extract information that may be helpful to determinate the nuclear matrix elements entering in the expression of neutrinoless double beta decay half-life. The strategies adopted in the experimental campaigns performed at INFN - Laboratori Nazionali del Sud are briefly described, emphasizing the advantages of the multi-channel approach to nuclear reaction data analysis