Nucleon Transfer Research Articles

Study of one-step and two-step neutron transfer in the reaction 6Li + 9Be* *Supported by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (AP19677087) and by the Russian Science Foundation (24-22-00117)

This paper presents the results of experiments conducted to measure the cross-sections for elastic scattering and nucleon transfer channels in the 6Li+9Be reaction at an incident energy of 68 MeV: 9Be(6Li,6Li)9Be, 9Be(6Li,7Li)8Be, 9Be(6Li,7Li)8Be2+, 9Be(6Li,8Li)7Be, and 9Be(6Li,7Be)8Li. The objective of the study is to elucidate the manifestation of the cluster structure of 9Be. Theoretical analysis of the contributions of the one-step and two-step neutron transfer mechanisms is performed using the distorted wave Born approximation method with the Fresco code. Good agreement between the calculations and the experimental data is obtained for the channels of elastic scattering 9Be(6Li,6Li)9Be, neutron 9Be(6Li,7Li)8Be, and proton transfer 9Be(6Li,7Be)8Li, as well as for the transfer of two neutrons 9Be(6Li,8Li)7Be. The dineutron cluster transfer mechanism makes a dominant contribution to the 9Be(6Li,8Li)7Be reaction channel at forward angles.

Recent results in the study of the 20Ne + 130Te collision within the NUMEN project and future perspectives

The NUMEN (Nuclear Matrix Elements for Neutrinoless double beta decay) project aims to investigate specific heavy–ion double charge exchange reactions to provide experimentally data driven information about nuclear matrix elements of interest in the context of neutrinoless double beta decay (0νββ). Taking into consideration that 130Te is a candidate nucleus for double beta decay, the 20Ne + 130Te system was experimentally investigated in a multi-channel approach by measuring the complete net of reaction channels, namely elastic and inelastic scattering, double charge exchange, single charge exchange, one– and two–nucleon transfer reactions, characterized by the same initial state interaction. The relevant experimental campaign was carried out at INFN – Laboratori Nazionali del Sud (LNS) in Catania using the Superconducting Cyclotron to accelerate the beams and the MAGNEX magnetic spectrometer to detect the reaction ejectiles. The experimental challenges and the obtained results for the 20Ne + 130Te system are presented and discussed. Since a deeper investigation of the 130Te nucleus as well as all the nuclei which are candidates for 0νββ decay is foreseen within the next phase of NUMEN, the Research and Development activity relevant to the facility upgrade is also discussed.

Suppressed electric quadrupole collectivity in 49Ti

Single-step Coulomb excitation of 46,48,49,50Ti is presented. A complete set of E2 matrix elements for the quintuplet of states in 49Ti, centred on the 2+ core excitation, was measured for the first time. A total of nine E2 matrix elements are reported, four of which were previously unknown. 2249Ti27 shows a 20% quenching in electric quadrupole transition strength as compared to its semi-magic 2250Ti28 neighbour. This 20% quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the 49Ti-50Ti pair (i.e., approximate single-j0f7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.

The slopes of sub-barrier heavy-ion fusion excitation functions shed light on the dynamics of quantum tunnelling

Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} in relation to their first energy derivatives d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document}. The relation between d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document} and Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.

Effect of the charge asymmetry and orbital angular momentum in the entrance channel on the hindrance to complete fusion

The hindrance to complete fusion is studied as a function of the charge asymmetry of colliding nuclei and orbital angular momentum of the collision. The formation and evolution of a dinuclear system (DNS) in the heavy-ion collisions at energies near the Coulomb barrier is calculated in the framework of the DNS model. The DNS evolution is considered as nucleon transfer between its fragments. The results prove that a hindrance at formation of a compound nucleus (CN) is related with the quasifission process, which is breakup of the DNS into products instead to reach the equilibrated state of the CN. The role of the angular momentum in the charge (mass) distribution of the reaction products for the given mass asymmetry of the colliding nuclei has been demonstrated. The results of this work have been compared with the measured data for the quasifission yields in the C12+Pb204 and Ca48+Er168 reactions to show the role of the mass asymmetry of the entrance channel. Published by the American Physical Society 2024

The 50th anniversary of the coupled channels Born approximation (CCBA) and the coupled reaction channels (CRC) theories of nucleon transfer reactions (a unique interplay between theory, experiment and computer technology, conducted during the most tumultuous period in modern American society)

Nucleon transfer reactions have played a fundamental role in understanding the single-particle components, shell structure and collective properties of atomic nuclei. The conventional distorted wave Born approximation (DWBA) envisioned the nucleon transfer reaction as a one-step process, which proceeds directly from the ground state of the target nucleus to a state of the residual nucleus. The coupled channels Born approximation (CCBA) and coupled reaction channels (CRC) theories evolved because a number of nucleon transfer reaction cross sections could not be reconciled within the DWBA. These coupled channels models revealed that, in addition to the “one-step” process of the DWBA, “multi-step” nucleon transfer processes involving accessary pathways can participate in populating the final nuclear state. In the CCBA, the auxiliary pathways involved inelastic excitations of the target and/or residual nucleus, whereas, in the CRC, the pathways included sequential nucleon transfer passing through nuclear states of an intermediate partition. Coherent addition of contributions from one-step and multi-step nucleon transfer processes resulted in dramatic alterations in reaction cross sections, which were experimentally confirmed. The CCBA and CRC linked the structure of the nuclei participating in a reaction to modalities of nucleon transfer arising during the relative motion between the interacting ions. These complementary theories inexorably changed physicists’ interpretations of nucleon transfer reactions and, in doing so, heralded in the new field of direct heavy-ion reactions.

Interplay of breakup and fusion in near-barrier collisions of weakly-bound nuclides

Light, weakly-bound nuclides such as 6,7Li and 9Be exhibit a diverse range of near-barrier reaction phenomena. Complete fusion is found to be suppressed by up to 35% with respect to barrier-passing model calculations. Their weak binding leads to significant breakup through excitation of the continuum, but also through production of weakly-bound or unbound neighbouring nuclides via nucleon transfer. Such systems also exhibit large yields of incomplete fusion, which is correlated empirically with cluster breakup thresholds for these stable nuclides. Disentangling these reaction phenomena and their complex interplay is one of the most interesting challenges in near-barrier reaction dynamics. Here we briefly review our recent progress in understanding the interplay between breakup and fusion. These results strongly suggest that the dominant mechanism leading to incomplete fusion and the suppression of complete fusion is direct capture of the projectile cluster constituents by the target nucleus, rather than requiring projectile breakup prior to fusion.

Insights from multinucleon transfer reactions in 206Pb+118Sn

Multinucleon transfer reactions for the 206Pb +118 Sn system were measured at Elab = 1200 MeV using the PRISMA large solid-angle magnetic spectrometer. The experiment was conducted at laboratory angles around the grazing angle, covering an angular range of approximately 20°. The resulting differential and total cross sections, along with Q-value distributions for various neutron and proton pick-up and stripping channels, are presented. The Q-value distributions suggest a transition from quasi-elastic to deep inelastic collision processes, particularly in channels involving nucleon transfers. The experimental results have been compared with GRAZING code calculations, showing good agreement for few-nucleon transfer channels, while channels with large nucleon transfers are underestimated, indicating the involvement of more complex processes.

Nucleon and delute cluster transfer in the reactions 6Li + 9Be

The results of experiments on studying nucleon and cluster transfer processes in the reactions of the 6Li (68 MeV) ions with the 9Be target nuclei are presented. The angular distributions for the reaction channels 9Be(6Li,α)11Bg.s and 9Be(6Li,10B)5Heg.s. have been measured. To describe the possible contributions of sequential transfer of nucleons and alpha clusters, as well as direct transfer of the 5Не cluster, the DWBA method (FRESCO) is used, the spectroscopic amplitudes are obtained for the configurations of (9Be+d) and (6Li+5He) in the 11B nucleus and (6Li+α) in the 10B nucleus. The results of the theoretical analysis agree with the experimental data and indicate a strong correlation between a neutron and an α-cluster, leading to the formation of the 5Не cluster in the transfer processes.

Recent results on the analysis of the 18O+48Ti collision at 275 MeV: Single charge exchange reaction

The present work is inherent to the NUMEN project that aims at providing data-driven information for the nuclear matrix elements of the neutrinoless double beta decay through the study of heavy-ion induced double charge exchange reactions. This is a formidable task since during a nuclear collision, the same final states may be populated through various reaction mechanisms. In this respect, understanding the degree of competition between successive nucleon transfer and charge exchange reactions is crucial for the proper description of the meson-exchange mechanism. To this purpose, the reaction dynamics in the 18O+48Ti collision were sought by measuring a plethora of reaction channels under the same experimental conditions. The 48Ti was chosen as target since it is the daughter nucleus of 48Ca in double beta decay. The relevant experiment was performed at the MAGNEX facility of INFN-LNS in Catania. In this contribution, the status of the analysis for the 48Ti(18O,18F)48Sc single charge exchange reaction will be presented.

Study of single-nucleon transfer reactions in the 18O+48Ti collision at 275 MeV

The study of single-nucleon transfer reactions for the 18O+48Ti system was pursued at the energy of 275 MeV as part of a more systematic study which is undertaken within the NUMEN and NURE experimental campaigns. The aim is to measure the complete set of available reaction network which are characterized by the same initial and final-state wavefunctions as the more suppressed double charge exchange reactions. Understanding the degree of competition between successive nucleon transfer and double charge exchange reactions is crucial for the description of the meson-exchange mechanism. In this respect, angular distribution measurements for one- and twonucleon transfer reactions for the 18O+48Ti system were carried out at theMAGNEX facility of INFN-LNS in Catania. An overview of the data analysis for the 48Ti(18O,19F)47Sc and 48Ti(18O,17O)49Ti reactions will be presented.

Analysis of reaction dynamics considering MAD by Langevin equation

In heavy ion fusion and nucleon transfer reactions, which lead to the synthesis of superheavy elements, it is important to understand the reaction mechanisms. The fusion reaction mechanism is analyzed in the case of deformed target nuclei such as actinide target nuclei. We have analyzed the correlation between fission fragment mass and scattering angle (MAD) using the Langevin equation. Taking into account the effect of the collision direction between the projectile and deformed target nuclei, we present the analysis of the experimental data for the MAD of 32S+232Th.

Pauli energy contribution to nucleus-nucleus interaction

The investigation delves into understanding how the Pauli exclusion principle influences the bare potential between atomic nuclei through the application of advanced theoretical methodologies. Specifically, the application of the novel Frozen-Hartree-Fock (DCFHF) technique is employed. The resulting potentials demonstrate a noticeable repulsion at short distances, attributed to the effects of the Pauli exclusion principle. To account for dynamic phenomena, such as nucleon transfer processes, the density-constrained time-dependent Hartree-Fock (DC-TDHF) method is utilized. This approach integrates isovector contributions into the potential, shedding light on their influence on fusion reactions. Notably, the inclusion of isovector effects leads to a reduction or enhancement in the inner part of the potential, suggesting a nuanced role of transfer in the fusion process.

Examining the influence of phonon coupling and nucleon transfer channels in reactions $$^{34,36}$$S + $$^{58}$$Ni, $$^{32,36}$$S + $$^{110}$$Pd and $$^{40,48}$$Ca + $$^{90}$$Zr around Coulomb barrier energies

Examining the influence of phonon coupling and nucleon transfer channels in reactions $$^{34,36}$$S + $$^{58}$$Ni, $$^{32,36}$$S + $$^{110}$$Pd and $$^{40,48}$$Ca + $$^{90}$$Zr around Coulomb barrier energies

Fabrication and characterization of CaF2 target for multi-nucleon transfer reaction studies

Thin CaF2 targets with carbon backing are fabricated for the first time using physical vapour deposition technique at the target laboratory of IUAC, New Delhi to perform a multi nucleon transfer reaction on 10,11B＋40Ca systems using General Purpose Scattering Chamber (GPSC) facility. Ca being an oxidizing material, we have used molecular CaF2 as the target material instead of Ca. Using turbo-molecular pump based coating unit (TMPU), carbon is deposited on cleaned glass slide and then CaF2 is deposited on diffusion pump based coating unit (DPU). We are successful in fabricating CaF2 targets of thickness ≈264.4μg/cm2 on carbon backing of thickness ≈21.5μg/cm2. The thickness and purity measured by the crystal thickness monitor equipped with the vacuum chamber is verified by different techniques like alpha energy loss, Rutherford Back Scattering (RBS), Electron Diffraction Spectroscopy (EDS) and X-ray Diffraction (XRD). Small impurity level were smeared during the observation and the target is successfully used for nuclear reaction experiment. The fabrication of molecular Ca target is found to be more conducive to experimentation since they exhibit less oxidation and herewith we discuss about fabrication technique, experimentation and characterization.

A multi–channel study of the 20Ne + 130Te system within the NUMEN project

The NUMEN project 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 (0νββ). In particular, it was proposed to use heavy – ion induced double charge exchange reactions as tools towards the determination of information on the nuclear matrix elements of 0νββ, strongly motivated by a number of similarities between the two processes. To this extent, the 20Ne + 130Te system was experimentally investigated in a multi-channel approach by measuring the complete net of reactions channels, namely double charge exchange, single charge exchange, elastic and inelastic scattering, one – and two – nucleon transfer reactions, characterized by the same initial projectile and target nuclei. The goal of the study is to fully characterize the properties of the nuclear wavefunctions entering in the 0νββ decay nuclear matrix elements. The experimental setup, the data reduction and some of the obtained results for the 20Ne + 130Te system will be presented and discussed.

Recent results on the analysis of the 48Ti(18O, 20Ne)46Ca reaction at 275 MeV

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 of investigating the complete reaction network potentially involved in the 48Ti→48Ca double charge exchange transition. Understanding the degree of competition between successive nucleon transfer and double charge exchange reactions is crucial for the description of the meson exchange mechanism. Into this context, angular distribution measurements for one- and two-nucleon transfer reactions for the system 18O+48Ti were performed at the MAGNEX facility of INFN-LNS in Catania. An overview of the status of the analysis for the two-proton transfer reaction will be given.

Effects of deuteron breakup and nucleon-transfer reactions on d+^{11}B elastic scattering

A set of experimental data consisting of angular distributions of d+^{11}B elastic and inelastic scattering and (d,t) reaction obtained at deuteron energy of 14.5 MeV as well as data sets for (d,p) (E_d = 21.5 MeV), (d,n) (E_d = 15.4 MeV) and (d,^3He) (E_d = 11.8 MeV) nucleon transfer reactions were analysed using the continuum-discretized coupled-channel (CDCC) and coupled-reaction channel (CRC) methods. It was found that at forward scattering angles the elastic scattering data are well described by parameter-free CDCC calculations which include breakup of the deuteron, but at more backward angles virtual effects due to target excitation and neutron-transfer reactions play an important role. The strongest effects are due to the excitation of ^{11}B and the neutron pickup reaction, reflecting their large cross sections. The effects induced by proton-transfer reactions are found to be negligible.

Production of 99Mo in inverse kinematics heavy ion reactions

Following the successful production of the radioimmunotheranostic nuclide 67Cu through the reaction of a 70Zn beam on a hydrogen gas target, our interest turned to the 99Mo/99mTc generator system. We produced 99Mo in inverse kinematics, with a100Mo beam at 12.0 MeV/nucleon impinging on a 4He gas target. The gas target was kept at liquid nitrogen temperature and pressures of 0.134(3), 0.280(6) and 1.33(3) atm. The produced isotopes and the beam were collected on a thick Al catcher foil. The 99Mo radioisotope can be produced in a one nucleon transfer occurring in peripheral reactions. Two competing factors determine the yield in such reactions, one is the cross-section which favors high mass targets, the other is the effective range which favors low-mass targets. Thus, at low 4He densities, higher beam energy at the exit of the gas target, most of the 99Mo production is generated in the Al foil, while at higher densities, most is generated in the gas target. The activity obtained at the end of the bombardment (given in Becquerel per particle nano-Amps per hour of irradiation), including the 4He gas and Al catcher contribution, were determined as 4.8(14), 2.5(7) and 3.8(11) kBq/(pnAh) for ρgas = 0.83, 0.18 and 0.09 mg/cm3, respectively. These results are competitive to other accelerator production methods; however, the method reported has the additional advantages of needing significantly less amount of expensive enriched isotope and offers an easier and cleaner collection/separation method.

Advances in nuclear structure via charged particle reactions with AGATA

In recent decades, gamma -ray spectroscopy has undergone a major technological leap forward, namely the technique of gamma -ray tracking, and has attained a sensitivity that is two orders of magnitude larger than that provided by the former generation of Compton-shielded arrays. Indeed the gain is comparable with the achievements since the dawn of gamma -ray spectroscopy. Such sensitivity can be further heightened by coupling gamma -ray spectrometers to other detectors that record complementary reaction products such as light-charged particles for transfer reactions and scattered ions for Coulomb excitation measurements. Nucleon transfer reactions offer an excellent mean to probe the energies of shell model single-particle orbitals and to study migration in energy of these orbitals as we venture away from stability. Such measurements can also estimate the cross sections of processes relevant to stellar evolution and nucleosynthesis. The measurement of gamma rays in coincidence with particles provides also information on the decay channel for unbound systems, which constitutes a useful input for astrophysics and nuclear structure near the drip-lines. Coulomb-excitation studies make it possible to infer collective structure in nuclei and to extract deformation properties of, in particular, open-shell systems. Here, selected examples will be presented, highlighting the power of these types of experiments when gamma -ray observation is included. The development of the experimental methods is reviewed, showing the results achieved before the advent of gamma -ray tracking. Examples of more recent experiments that have successfully exploited gamma -ray tracking with AGATA are then presented as showcases for the outstanding performance of the composite detection systems. The outlook for experiments using newly developed devices such as GRIT and other detectors such as SPIDER is described.