Search

The present paper is focused on our recent efforts to study the production and identification of neutron-rich medium-mass rare isotopes from peripheral reactions at beam energies around and below the Fermi energy. We obtained high-quality experimental data from a recent experiment with the MAGNEX spectrometer at the INFN-LNS in Catania, Italy. The main aim of this experiment was to check the feasibility of ejectile identification in this energy regime with the use of a large acceptance magnetic spectrometer. Our developed technique for particle identification depends mainly on a reconstruction of both the atomic number Z and the ionic charge q of the ions, followed by the identification of the mass. Our method was successfully applied to identify neutron-rich ejectiles from multinucleon transfer from the reaction of 70Zn (15 MeV/nucleon) + 64Ni. Preliminary results indicate that the extracted experimental distributions, along with comparisons with the theoretical models could help us to shed light to the complex reaction mechanism of multinucleon transfer in this energy regime.

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.

We present the status of the ASPECT-BET (An sdd-SPECTrometer for BETa decay studies) project which is aimed at developing a new detection strategy to perform high-precision, high-accuracy measurements of the energy spectra of beta decays of interest for the physics community, in particular in the field of nuclear physics, double beta decay and reactor neutrinos. The aim is to exploit a relatively novel spectroscopic technique based on Silicon Drift Detectors. An SDD-spectrometer, equipped with all the ancillary detectors required to reject events with only a partial energy deposition in the main sensitive elements, will provide high-statistics and virtually zero-background data. In order to isolate and study the systematic uncertainties, the statistical error on the measured spectra has to be reduced to a negligible level, balancing source activity, measurement duration and background. Reliable and well understood Montecarlo simulations are a key component of this application, as they provide a model for the response functions of the spectrometer, to be deconvolved from the data in order to correctly reconstruct the original spectral shapes. Thanks to the flexibility of the SDD detector technology, the here presented spectrometer could be coupled to a variety of beta sources, ranging from nuclei deposited on the surface of SDDs to minimise source self-absorpion to short-lived isotopes created and collected at unstable isotope beams like ISOLDE at CERN or the exotic beams at LNS, Catania. The current status of the technology, as well as some preliminary sensitivity studies, are presented and discussed.

The 130Te(20Ne,20O)130Xe double charge exchange reaction was measured for the first time at very forward angles with the MAGNEX magnetic spectrometer at INFN-LNS. The study, performed at beam energy of 306 MeV, is part of a systematic exploration promoted by the NUMEN project. The last aims to measure specific reaction cross sections to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double beta decay.

International audience; 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.

Two-nucleon transfer reactions are essential tools to investigate specific features of the nuclear structure, such as the correlation among valence particles in the transfer process. Besides, transfer reactions may be an important channel to take into account in charge-exchange processes since they can represent a competing contribution to the final cross section. The two-proton pickup transfer reaction $^{40}\mathrm{Ca}(^{18}\mathrm{O},^{20}\mathrm{Ne})\phantom{\rule{0.16em}{0ex}}^{38}\mathrm{Ar}$ has been measured at 270 MeV, and the angular distributions for transitions to different excited states extracted. This paper shows the analysis of the data performed by finite-range coupled reaction channel and coupled-channel Born approximation methods. Extensive shell-model calculations are performed to derive the one- and two-proton spectroscopic amplitudes for the projectile and target overlaps. The role of the simultaneous and sequential two-proton transfer mechanisms to populate the measured final states or groups of states, mainly characterized by a high collectivity, is also discussed.

The search for neutrinoless double-beta (0νββ) decay is currently a key topic in physics, due to its possible wide implications for nuclear physics, particle physics, and cosmology. The NUMEN project aims to provide experimental information on the nuclear matrix elements (NMEs) that are involved in the expression of 0νββ decay half-life by measuring the cross section of nuclear double-charge exchange (DCE) reactions. NUMEN has already demonstrated the feasibility of measuring these tiny cross sections for some nuclei of interest for the 0νββ using the superconducting cyclotron (CS) and the MAGNEX spectrometer at the Laboratori Nazionali del Sud (LNS.) Catania, Italy. However, since the DCE cross sections are very small and need to be measured with high sensitivity, the systematic exploration of all nuclei of interest requires major upgrade of the facility. R&amp, D for technological tools has been completed. The realization of new radiation-tolerant detectors capable of sustaining high rates while preserving the requested resolution and sensitivity is underway, as well as the upgrade of the CS to deliver beams of higher intensity. Strategies to carry out DCE cross-section measurements with high-intensity beams were developed in order to achieve the challenging sensitivity requested to provide experimental constraints to 0νββ NMEs.

International audience; 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.

The40Ca(18O,18F)40K single charge exchange (SCE) reaction is explored at an incident energy of 275 MeV and analyzed consistently by collecting the elastic scattering and inelastic scattering data under the same experimental conditions. Full quantum-mechanical SCE calculations of the direct mechanism are performed by including microscopic nuclear structure inputs and adopting either a bare optical potential or a coupled channel equivalent polarization potential (CCEP) constrained by the elastic and inelastic data. The direct SCE mechanism describes the magnitude and shape of the angular distributions rather well, thus suggesting the suppression of sequential multi-nucleon transfer processes.

NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross-section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the fact that the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave functions in the two types of processes and the formal similarity of the transition operators. The main experimental tools for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer at the INFN-LNS laboratory. However, the tiny values of DCE cross-sections and the resolution requirements demand beam intensities much higher than those manageable with the present facility. The on-going upgrade of the INFN-LNS facilities promoted by the POTLNS a project in this perspective is intimately connected to the NUMEN project. This paper describes the solutions proposed as a result of the R&D activity performed during the recent years. The goal is to develop suitable technologies allowing for the measurements of DCE cross-section under extremely high beam intensities. a PIR01_00005 — potenziamento dell’infrastruttura di ricerca Laboratori Nazionali del Sud per la produzione di fasci di ioni ad alta intensitá.

The 4He(4He,4He)4He* inelastic scattering was revisited in a new coincidence measurement at the MAGNEX facility of Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud. The 4He + 4He → 4He + 4He* → 4He + 3H + 1H and 4He + 4He → 4He + 4He* → 4He + 3He + n reactions were measured simultaneously by detecting the 4He particles at the MAGNEX magnetic spectrometer in coincidence with the 3H and 3He at the OSCAR silicon telescope. The main concept of the experiment is described and the data reduction strategy is reported.

The 18O+48Ti reaction was studied at the energy of 275 MeV for the first time under the NUMEN and NURE experimental campaigns with the aim to investigate the complete net of reaction channels potentially involved in the 48Ca→48Ti double charge exchange transition. Such a transition is of great interest because of its relevance to the extraction of 48Ca→48Ti double beta decay nuclear matrix element. The relevant experiment was carried out at the MAGNEX facility of INFN-LNS in Catania. Angular distribution measurements for the various reaction products were performed by using the MAGNEX large acceptance magnetic spectrometer. The present contribution is focused on the analysis of the one-proton transfer channel with emphasis on the particle identification technique and the estimation of background contaminations.

Double 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.

Background: In our recent experiment, $^9$Be+p at 5.67A MeV, the breakup decay rates to the 3 configurations, $\alpha$+$\alpha$+n, $^8$Be$^*$+n and $^5$He+$^4$He of $^9$Be, were observed and quantified, in a full kinematics approach. Unfolding step by step the accessibility to the above configurations, it will require similar studies at lower and higher energies as well as the interpretation of the data in a theoretical framework. Purpose: Investigate the breakup decay rate of $^9$Be+p at 2.72A MeV, where the $\alpha$+$\alpha$+n configuration is mainly accessible. Compare and interpret data at 2.72A MeV and 5.67A MeV into a 4-body CDCC formalism; Point out and discuss couplings to continuum. Methods: Our experimental method includes an exclusive breakup measurement in a full kinematic approach of $^9$Be incident on a proton target at 2.72A MeV, together with elastic scattering and other reaction channels measurements under the same experimental conditions. The interpretation of the data at 2.72A MeV and 5.67A MeV is considered in a 4-body CDCC approach, using the Transformed Harmonic Oscillator method for the 3-body projectile. Results: An elastic scattering angular distribution at 2.72A MeV is measured, which compares very well with CDCC calculations, indicating a strong coupling to continuum. At the same energy, the measured breakup and total reaction cross sections present good agreement with the calculated values. Further on, the elastic scattering and breakup cross section data at 5.67A MeV are found in very good agreement with the CDCC calculations. The present results support further our 3-body model for the structure of $^9$Be, validating relevant radiative reaction rates obtained previously.

Background: Heavy-ion induced two-nucleon transfer reactions are powerful tools to reveal peculiar aspects of the atomic nucleus, such as pairing correlations, single-particle and collective degrees of freedom, and more. Also, these processes are in competition with the direct meson exchange in the double charge exchange reactions, which have recently attracted great interest due to their possible connection to neutrinoless double-beta decay. In this framework, the exploration of two-nucleon transfer reactions in the 20Ne+116Cd collision at energies above the Coulomb barrier is particularly relevant since the 116Cd nucleus is a candidate for the double-beta decay. Methods: We measured the excitation energy spectra and absolute cross sections for the two reactions using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. We performed direct coupled reaction channels and sequential distorted wave Born approximation calculations using the double folding S\~ao Paulo potential to model the initial and final state interactions. The spectroscopic amplitudes for two- and singleparticle transitions were derived by different nuclear structure approaches: microscopic large-scale shell model, interacting boson model-2 and quasiparticle random phase approximation. Results: The calculations are able to reproduce the experimental cross sections for both two-neutron and twoproton transfer reactions. The role of couplings with the inelastic channels are found to be important in the two-proton transfer case. A competition between the direct and the sequential process is found in the reaction mechanism. For the two-proton transfer case, the inclusion of the 1g7/2 and 2d5/2 orbitals in the model space is crucial.

The Gamow–Teller strength distributions of $${^{116} \text {Sb}}$$116Sb and $${^{122} \text {Sb}}$$122Sb were measured with the $${^{116,122} \text {Sn} (^{3} \text {He},t) ^{116,122} \text {Sb}}$$116,122Sn(3He,t)116,122Sb charge-exchange reactions at $${140 \ \text {MeV/u}}$$140MeV/u. The measurements were carried out at the Research Center for Nuclear Physics (RCNP) at Osaka University in Osaka, Japan using the Grand Raiden spectrometer. The data were analysed by Multipole-Decomposition Analysis (MDA). The Gamow–Teller strengths summed up to $${28 \ \text {MeV}}$$28MeV are $${(38 \pm 7) \%}$$(38±7)% and $${(48 \pm 6) \%}$$(48±6)% of the Ikeda sum rule for $${^{116} \text {Sb}}$$116Sb and $${^{122} \text {Sb}}$$122Sb, respectively, if the quasi-free scattering (QFS) contribution is not subtracted. These percentages are $${(29 \pm 7) \%}$$(29±7)% and $${(35 \pm 5) \%}$$(35±5)%, respectively, if the QFS contribution is maximally subtracted. These results were compared to those from previous measurements of the same isotopes, to recent measurements of $${^{150} \text {Pm}}$$150Pm, and to a Quasi-particle Random-Phase Approximation (QRPA) calculation with Quasi-Particle Vibration Coupling (QPVC). The data suggest that the true QFS contribution is small for $${^{116} \text {Sb}}$$116Sb, but are inconclusive about whether the QFS contribution is small or significant for $${^{122} \text {Sb}}$$122Sb. Therefore, these data may provide an interesting test for the general quenching phenomenon of the Gamow–Teller Resonance (GTR). However, more research to reveal the nature of the QFS contribution is still needed on both the experimental and the theoretical side.

The 9Be(18O,16O)11Be two-neutron transfer reaction at 84 MeV is measured at forward angles to explore the continuum of 11Be nucleus. Transfer-to-the-continuum (TC) reaction calculations are applied using for the first time an ab-initio S-matrix. It is derived from the ab-initio no-core shell model with continuum (NCSMC) method, recently used to describe the bound and continuum spectrum of 11Be. Previously known levels are confirmed and theoretical and experimental evidence for a 9/2+ state at Ex = 5.8 MeV is given, whose configuration is thought to be 10Be(2+) + n(d5/2).

Nuclear matrix elements (NMEs) for double beta decays (DBDs) are crucial for studying the neutrino mass and other neutrino properties beyond the standard electro-weak model by measuring neutrino-less DBDs. The spin-dipole (SD) J π = 2- NME is one of the major components associated with the DBD NME. The SD NME for 76Ge was derived for the first time by using the 74,76 Ge (3He, t) at RCNP Osaka. The obtained SD NME for the 76Ge → 76As ground-state transition is in natural units. This is smaller by a coefficient around k ≈ 0.2 with respect to the quasi-particle model NME. The impact of the reduced (quenched) SD NME on DBD neutrino studies is discussed.

Physics cases of increasing interest in the recent years, such as the study of double charge exchange reactions for neutrino physics, require the study of very suppressed reaction channels in medium-heavy ion induced nuclear reactions. The main experimental challenges are the possibility to identify and detect the medium-heavy quasi-projectiles and the capability to measure very low cross-sections (few nb) with high sensitivity at very forward angles, including zero degree. The experimental techniques adopted in the setup of the MAGNEX magnetic spectrometer to face these issues are described in this paper., arXiv admin note: substantial text overlap with arXiv:1811.08693

The NURE (NUclear REactions for neutrinoless double beta decay) project has been selected for receiving funding in the call Starting Grant 2016 of European Research Council (ERC). The project, which takes advantage of nuclear physics methods to give a contribution to the neutrino physics, has a duration of 5 years. A key aspect is the use of the K800 Superconducting Cyclotron, for the acceleration of the required high resolution and low emittance heavy-ion beams, and of the MAGNEX large acceptance magnetic spectrometer, for the measurement of the reaction cross sections. These facilities are in operation at INFN Laboratory Nazionali del Sud in Catania (Italy).

Signatures of the population of the Giant Pairing Vibration (GPV), a correlated two-nucleon excitation across major shell expected to be populated in two-nucleon transfer reactions, have been observed for the first time in carbon isotopes. In the present paper, a review of the experimental methods and of the analysis leading to that observation is reported. A new case, with new experimental data, regarding the possible population of the GPV in another light nucleus, 11Be , by the same reaction, is introduced and discussed.

In this work we investigate whether it is feasible with proton inelastic scattering in inverse kinematics to quantify breakup decay rates, by observing the proton recoil in a full kinematics approach. Taking as example the 2.43 MeV excited state of 9Be, we perform an exclusive breakup measurement of 9Be incident on a proton target at an energy of 51 MeV. Two of the three cluster constituents (α and α) as well as the proton target recoil are recorded in a triple coincidence mode. As in other methods we have determined relative α − α and α − n , Q-value and 9Be excitation spectra, energy spectra for all fragments observed and non observed, reconstructed in a full kinematics approach. Additionally to that, we have obtained and concentrated on energy spectra of the proton recoil. The signature of the 9Be configurations were identified in bi-dimensional Δ E − E spectra (proton contour) and decay rates were determined for all three configurations He 5 + α , Be 8 + n and α + α + n . Finally a breakup cross section was deduced as σ b r e a k = ( 142 ± 20 ) mb . We conclude that proton inelastic excitation to continuum of Borromean light nuclei in inverse kinematics, may provide the mean for probing in the proton recoil spectra the decay rates through all cluster configurations. This involves extensive simulations with the implementation of the experimental conditions and of calculations describing the physics in continuum.

Background: Double charge exchange (DCE) nuclear reactions have recently attracted much interest as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. In this framework, a good description of the reaction mechanism and a complete knowledge of the initial and final-state interactions are mandatory. Presently, not enough is known about the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for future DCE studies. Among these, the Ne20+Ge76 DCE reaction is particularly relevant due to its connection with Ge76 double-β decay. Purpose: We intend to characterize the initial-state interaction for the Ne20+Ge76 reactions at 306 MeV bombarding energy and determine the optical potential and the role of the couplings between elastic channel and inelastic transitions to the first low-lying excited states. Methods: We determine the experimental elastic and inelastic scattering cross-section angular distributions, compare the theoretical predictions by adopting different models of optical potentials with the experimental data, and evaluate the coupling effect through the comparison of the distorted-wave Born approximation calculations with the coupled channels ones. Results: Optical models fail to describe the elastic angular distribution above the grazing angle (≈9.4∘). A correction in the geometry to effectively account for deformation of the involved nuclear systems improves the agreement up to about 14∘. Coupled channels effects are crucial to obtain good agreement at large angles in the elastic scattering cross section. Conclusions: The analysis of elastic and inelastic scattering data turned out to be a powerful tool to explore the initial and final-state interactions in heavy-ion nuclear reactions at high transferred momenta.

International audience; A complete study of the 6,7Li + p reactions was performed by measuring the complete net of reaction channels at the energy range of ∼ 2 to 5 MeV/nucleon. The experiments were performed at the MAGNEX facility of the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) in Catania. The breakup channel was identified by means of a new algorithm, MULTIP, which gives the possibility of following up the decay of the nucleus into two or more constituent particles from the rest frame of the nucleus itself to the laboratory frame. Angular distributions were obtained for all reaction products and were considered within the Continuum Discretized Coupled Channels (CDCC) framework. The results of the CDCC calculations were found in a very good agreement with the experimental data presenting a strong evidence for the important influence of coupling to breakup on the elastic channel.

Recently, the bound and continuum spectrum of $^{11}\mathrm{Be}$ has been calculated within the ab initio no-core shell model with continuum (NCSMC) method, with the parity inversion in the ground state successfully reproduced. The continuum spectrum obtained is in agreement with known experimental levels. The S matrix contained in the NCSMC continuum wave functions of the $\mathrm{n}+^{10}\mathrm{Be}$ system is used in this work for the first time in a transfer-to-the-continuum (TC) reaction calculation. The TC approach is applied to study the excitation energy spectrum of $^{11}\mathrm{Be}$ measured in the $^{9}\mathrm{Be}(^{18}\mathrm{O},^{16}\mathrm{O})^{11}\mathrm{Be}$ reaction at 84 MeV. Previously known levels are confirmed and theoretical and experimental evidence for a 9/${2}^{+}$ state at ${E}_{x}=5.8$ MeV is given, whose configuration is thought to be $^{10}\mathrm{Be}({2}^{+})+\mathrm{n}({d}_{5/2})$.

The nuclear scattering at energies well above the Coulomb barrier allows for a fairly sensitive examination of the parameters of the optical potential when the relevant couplings are included into the calculations. In this work we present experimental angular distribution data for the elastic and inelastic scatterings of $^{16}$O impinging on $^{27}$Al and $^{28}$Si target nuclei at \textit{E}$_{lab}=240$ MeV. The experimental data were measured at $7\degree < \theta_{c.m.} < 16\degree$ with good angular resolution. Experimental data are compared with coupled channel calculations with the inclusion of couplings to excited states in the target and projectile. We show that the shape of angular distributions are sensitive to the mass diffuseness parameter and the best agreement is achieved for $a = 0.62$ fm.

Elastic scattering and breakup angular distribution measurements for the systems 6,7Li + p were performed at the MAGNEX facility of the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) in Catania, in the energy range of (2.3-5.4)AMeV. The breakup channel was identified and quantified adopting the algorithm MULTIP.Within this algorithm which is a Monte Carlo simulation code, the history of the breakup fragments can be tagged from the rest frame of the decay nucleus itself to the laboratory frame. Angular distribution data of both elastic scattering and breakup were analyzed under the same theoretical model and the influence of continuum on the elastic channel was investigated., The research leading to these results was partially funded by the European Union Seventh Framework Programme FP7/2007-2013 (Grant Agreement No. 262010ENSAR) and also by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 714625).

An updated overview of recent results on Heavy-Ion induced reactions of interest for neutrinoless double beta decay is reported in the framework of the NUMEN project. The NUMEN idea is to study heavy-ion induced Double Charge Exchange (DCE) reactions with the aim to get information on the nuclear matrix elements for neutrinoless double beta (0νββ) decay. Moreover, to infer the neutrino average masses from the possible measurement of the half- life of 0νββ decay, the knowledge of the nuclear matrix elements is a crucial aspect. Uma visão geral atualizada dos resultados recentes sobre reações induzidas por íons pesados ​​de interesse para o decaimento beta duplo sem neutrinos é relatada na estrutura do projeto NUMEN. A ideia do NUMEN é estudar reações de Double Charge Exchange (DCE) induzidas por íons pesados ​​com o objetivo de obter informações sobre os elementos da matriz nuclear para o decaimento beta duplo sem neutrinos (0νββ). Além disso, para inferir as massas médias dos neutrinos a partir da possível medição da meia-vida do decaimento 0νββ, o conhecimento dos elementos da matriz nuclear é um aspecto crucial. 1308 012002

This work presents theoretical results compared with the experimental data for the two–neutron transfer angular distribution in which a beam of 18O nucleus, at 84 MeV incident energy, has collided onthe 13C, 28Si, and 64Ni targets. The two-neutron transfer in the 9Be(7Be,9Be)7Be reaction, at 23.1 MeV incident energy, was also analyzed. The main goal was to verify the relevance of the pairing correlation of the two transferred neutrons on the cross sections and to show its role when both neutrons are transferred to states with a low and high degree of collectivity.

International audience; New experimental measurements of charge state distributions produced by a 20Ne10+ beam at 15 MeV/u colliding on various thin solid targets are presented. The useof the MAGNEX magnetic spectrometer enabled measurements of the 8+ charge state down to fractions of a few 10−5. The use of different post-stripper foils locateddownstream of the main target is explored, showing that low Z materials are particularly effective to shift the charge state distributions towards fully strippedconditions. The dependence on the foil thickness is also studied and discussed.

In this work, we study the effect of paring correlation on the two-neutron transfer reaction \(^{28}\)Si(\(^{18}\)O,\(^{16}\)O)\(^{30}\)Si at 84 MeV incident energy in the laboratory frame. For this, coupled reaction channel (CRC) and coupled channel Born approximation (CCBA) calculations were performed considering the cluster, independent coordinates and sequential transfer models for two-neutron transfer. For the calculation of the spectroscopic amplitudes the NuShellX (http://www.garsington.eclipse.co.uk/, [1]) code was used.

International audience; NUMEN aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ), by high-accuracy measurements of the cross sections of Heavy Ion (HI) induced Double Charge Exchange (DCE) reactions. First evidence about the possibility to get quantitative information about NME from experiments is found for the (^18O,^18Ne) and (^20Ne,^20O) reactions. Moreover, to infer the neutrino average masses from the possible measurement of the half-life of 0νββ decay, the knowledge of the NME is a crucial aspect. The key tools for this project are the high resolution Superconducting Cyclotron beams and the MAGNEX magnetic spectrometer at INFN Laboratori Nazionali del Sud in Catania (Italy). The measured cross sections are extremely low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is foreseen in order to increase the experimental yield of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest.

Background: Recently, a systematic exploration of two-neutron transfer induced by the $(^{18}\mathrm{O},\phantom{\rule{0.16em}{0ex}}^{16}\mathrm{O})$ reaction on different targets has been performed. The high-resolution data have been collected at the MAGNEX magnetic spectrometer of the INFN-LNS Laboratory in Catania and analyzed with the coupled reaction channel (CRC) approach. The simultaneous and sequential transfers of the two neutrons have been considered under the same theoretical framework without the need for adjustable factors in the calculations.Purpose: A detailed analysis of the one-neutron transfer cross sections is important to study the sequential two-neutron transfer. Here, we examine the $(^{18}\mathrm{O},\phantom{\rule{0.16em}{0ex}}^{17}\mathrm{O})$ reaction on $^{16}\mathrm{O},\phantom{\rule{0.28em}{0ex}}^{28}\mathrm{Si}$, and $^{64}\mathrm{Ni}$ targets. These even-even nuclei allow for investigation of one-neutron transfer in distinct nuclear shell spaces.Method: The MAGNEX spectrometer was used to measure mass spectra of ejectiles and extract differential cross sections of one-neutron transfer to low-lying states. We adopted the same CRC formalism used in the sequential two-neutron transfer, including relevant channels and using spectroscopic amplitudes obtained from shell-model calculations. We also compare with the one-step distorted-wave Born approximation (DWBA).Results: For the $^{18}\mathrm{O}+^{16}\mathrm{O}$ and the $^{18}\mathrm{O}+^{28}\mathrm{O}$ systems, we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the $^{18}\mathrm{O}+^{64}\mathrm{Ni}$ system, we considered only one interaction, and the theoretical curve describes the shape and order of magnitude observed in the experimental data.Conclusions: Comparisons between experimental DWBA and CRC angle-integrated cross sections suggest that excitations before or after the transfer of a neutron are relevant in the $^{18}\mathrm{O}+^{16}\mathrm{O}$ and $^{18}\mathrm{O}+^{64}\mathrm{Ni}$ systems.

International audience; The article describes the main achievements of the NUMEN project together with an updated and detailed overview of the related R&D activities and theoretical developments. NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the fact that the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave functions in the two types of processes and the formal similarity of the transition operators. First experimental results obtained at the INFN-LNS laboratory for the$^{40}$Ca($^{18}$O,$^{18}$Ne)$^{40}$Ar reaction at 270MeV give an encouraging indication on the capability of the proposed technique to access relevant quantitative information. The main experimental tools for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer. The former is used for the acceleration of the required high resolution and low emittance heavy-ion beams and the latter is the large acceptance magnetic spectrometer for the detection of the ejectiles. The use of the high-order trajectory reconstruction technique, implemented in MAGNEX, allows to reach the experimental resolution and sensitivity required for the accurate measurement of the DCE cross sections at forward angles. However, the tiny values of such cross sections and the resolution requirements demand beam intensities much larger than those manageable with the present facility. The on-going upgrade of the INFN-LNS facilities in this perspective is part of the NUMEN project and will be discussed in the article.

An upgraded and improved version of the focal plane detector (FPD) of the large-acceptance magnetic spectrometer MAGNEX is described here. The FPD consists of a tracker operating at low pressure and of a silicon detector wall. Thanks to a different geometry of the electron multiplication and induction elements, the new detector guarantees a superior signal to noise ratio, resulting in a more accurate tracking and a cleaner identification of the detected heavy ions. The new detector has been tested by using a $^{18}$O beam at an energy of 84 MeV. A description of the new FPD that pinpoints the innovation and the obtained performances is given and discussed in details., 25 pages, 15 figures, submitted to Nuclear Instruments and Methods in Physics Research Section A

Simulations for estimating the neutron and γ-rays radiation background in the forthcoming NUMEN experiments at the upgraded MAGNEX facility were performed with the simulation package FLUKA. Three main radiation sources were considered in our simulations namely, the beam-target interaction, the moderation of the beam particles inside the beam dump and a hypothetical 10W loss in the beam intensity during the beam transport. In the present contribution, the results of this preliminary analysis are presented and discussed.