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We present an outlook of studies performed in collaboration or inspired by Prof. Mahir Hussein. The first part refers to the elastic scattering measurements performed in the 80–90 with α-structured systems with strong oscillations in the angular distributions and a large increase of the cross-sections at backward angles, an effect called Anomalous Large Angle Scattering (ALAS). The second part refers to the installation of the “Radioactive Ion Beams in BraSil” (RIBRAS) facility, which was an idea promoted by Prof. Hussein and became reality due to his strong support. It was installed in 2004 as the first radioactive ion beam facility in the southern hemisphere and it has been operating continuously since then. In this paper, we will describe the facility, and some interesting results obtained with the 2-neutron-halo, exotic 6He beam, provided by RIBRAS.

The $^{8}\mathrm{Li}+^{58}\mathrm{Ni}$ collision is investigated at 23.9, 26.1, 28.7, and 30 MeV bombarding energies. Quasielastic angular distributions and the singles $^{7}\mathrm{Li}$ angular and energy distributions are presented. Coupled-reaction channels (CRC) calculations, which include the coupling of the elastic channel to $^{59}\mathrm{Ni}=^{58}\mathrm{Ni}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}n$ states above and below the neutron threshold, provide a simultaneous description of the quasielastic and transfer distributions and evidence the strong effect of the one-neutron transfer/breakup channels on the quasielastic scattering. The $^{7}\mathrm{Li}$ angular and energy distributions have been also successfully analyzed combining the continuum discretized coupled channels (CDCC) method, for the elastic breakup, and the IAV model of Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)], for the nonelastic breakup. These calculations indicate that most of the $^{7}\mathrm{Li}$ yields are due to nonelastic breakup contributions (transfer), whereas elastic breakup plays a minor role.

Background: Reactions involving exotic and stable weakly bound nuclei have been extensively studied in recent years. Although several models have been successfully used to explain particular reaction outcomes, the answers to many questions remain elusive. In previous works, we presented elastic, inelastic, and transfer angular distributions for the $^{10}\mathrm{B}+^{120}\mathrm{Sn}$ system measured at ${E}_{\mathrm{Lab}}=31.5$, 33.0, 35.0, and 37.5 MeV. The data set was analyzed through coupled reaction channels calculations in the context of the double-folding S\~ao Paulo potential.Purpose: We investigate nuclear reaction mechanisms for systems involving weakly bound projectiles.Method: Angular distributions for several nuclear reaction processes were measured for the $^{10}\mathrm{B}+^{120}\mathrm{Sn}$ system at ${E}_{\mathrm{Lab}}=39.70$ MeV.Results: The new data set involves angular distributions for elastic scattering, projectile and target inelastic excitations, one-neutron pickup transfer, one-proton stripping transfer, deuteron pickup transfer, and $^{3,4}\mathrm{He}$ stripping transfer. We have also observed $^{10}\mathrm{Be}$ nuclei. The effect of the couplings to some nonelastic states on the angular distributions is discussed.Conclusion: The theoretical calculations within the coupled reaction channels formalism provide an overall good agreement with the corresponding inelastic, one-neutron stripping, one-proton pickup, one-deuteron pickup, and $^{3}\mathrm{He}$ stripping transfer data. However, to improve the description of the elastic scattering angular distribution, the inclusion of additional channels in the coupling scheme might be necessary.

The ECIS (Equations Couplees Iterations Sequentielles) code of Jacques Raynal continues to have an important role since its first version in the seventies. Its use to describe the elastic and inelastic scattering of light heavy ions at energies close to the Coulomb barrier is the first topic of this paper. Nuclear reactions with weakly bound stable and radioactive projectiles are described in the second topic, where the projectiles breakup is not taken into account in ECIS and a more recent formalism called Continuum Discretized Coupled Channels (CDCC) calculations is applied to them. The second topic also contains some results that were obtained at the Radioactive Ion Beams in Brasil (RIBRAS) facility, with a radioactive 2n-halo $$^6$$ He beam on light, medium mass, and heavy targets.

Experiments with secondary radioactive beams $$^6$$ He, $$^7$$ Be, $$^8$$ Li and $$^8$$ B on several targets have been performed in recent years at the Radioactive Ion Beams facility in Brasil (RIBRAS). We present results of elastic scattering and reaction measurements performed with this facility. A preliminary Coulomb excitation experiment using gamma-particle coincidence technique is described.

The $^{10}\mathrm{B}+^{197}\mathrm{Au}$ reaction has been investigated through cross-section measurements for different channels, such as quasielastic and elastic scattering, inelastic excitation of low-lying $^{197}\mathrm{Au}$ states, and one-neutron pickup and one-proton stripping transfer reactions. Experimental angular distributions were obtained for 20 bombardment energies around the Coulomb barrier: $38\ensuremath{\le}{E}_{lab}\ensuremath{\le}61\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Coupled reaction channels calculations have been performed in the context of the double-folding S\~ao Paulo potential, and details of the data analysis are discussed along the paper. In general, the theoretical calculations provide a satisfactory description of the data.

In a previous work, we presented data for the $^{10}\mathrm{B}+^{197}\mathrm{Au}$ system, corresponding to quasielastic and elastic scattering, $^{197}\mathrm{Au}$ inelastic excitation, and one neutron pickup transfer, measuring the angular distribution of scattered beam-like ejectiles at several energies around the Coulomb barrier. In this paper, we present data for the fusion process of the same system, at several energies around the Coulomb barrier, as well as new data for one neutron pickup and stripping transfer. In this case, we detected offline $\ensuremath{\gamma}$ rays stemming from the $\ensuremath{\beta}$-delayed decay chain of fusion-evaporation residues and heavy transfer products. As in our previous work, we analyzed this data set with coupled reaction channels calculations using the S\~ao Paulo potential. We show that the coupling to the one neutron transfer channel is quite important to describe the fusion data at the sub-barrier energy region. We also provide a comparison of the experimental fusion cross sections obtained for $^{10}\mathrm{B}+^{197}\mathrm{Au}$ with data for several other systems involving the same target nucleus.

Background: Neutron transfer measurements for the $^{18}\mathrm{O}+^{28}\mathrm{Si}$ system have shown that the experimental one-neutron and two-neutron transfer cross sections are well reproduced with spectroscopic amplitudes from two different shell-model interactions for the Si isotopes: psdmod for the two-neutron transfer, and psdmwkpn for the one-neutron transfer.Purpose: The need for two distinct shell-model interactions to reproduce two neutron-transfer processes in the same nuclei may cover a more complex mechanism in the one-neutron transfer that requires the unpairing of neutrons prior to its transfer in the ($^{18}\mathrm{O},^{17}\mathrm{O}$) reaction. Studying a nucleus where this characteristic is absent ($^{13}\mathrm{C}$) should help to elucidate this question.Method: One-neutron transfer cross sections were measured for the $^{13}\mathrm{C}+^{28}\mathrm{Si}$ at ${E}_{lab}=30$ and 34 MeV, and compared with coupled reaction channel calculations using spectroscopic amplitudes derived from the psdmod and psdmwkpn shell-model interactions.Results: The spectroscopic amplitudes from the psdmod interaction for the relevant states in $^{29}\mathrm{Si}$ provide a good description of the experimental data and the corresponding values agree with previous estimates obtained from the $(d,p)$ reaction.Conclusions: The experimental data for the one-neutron transfer to $^{28}\mathrm{Si}$ induced by ($^{13}\mathrm{C},^{12}\mathrm{C}$) reaction is well reproduced using spectroscopic amplitudes from the psdmod.

Alpha particle energy distributions in the 6He+120Sn collision have been measured at 7 bombarding energies above the Coulomb barrier. A phenomenological analysis of the centroids of the experimental distributions was performed and compared with the expected alpha-particle energies from breakup and neutron transfer reactions. Q-optimum conditions were determined using the Brinks formula for the di-neutron transfer reaction. A comparison of the measured alpha-particle production cross-sections with Continuum Discretized Coupled Channels (CDCC) calculations for breakup is presented. Fundacao de Amparo `a Pesquisa no Estado de Sao Paulo 2013/22100-7, 2014/19666-1 Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico 308935/2018-7 Ministerio de Economía y Competitividad FIS2017-88410-P European Union 654002

We present new experimental angular distributions for the elastic scattering of $^{6}\mathrm{Li}+^{120}\mathrm{Sn}$ at three bombarding energies. We include these data in a wide systematic involving the elastic scattering of $^{4,6}\mathrm{He},\phantom{\rule{0.16em}{0ex}}^{7}\mathrm{Li}$, $^{9}\mathrm{Be},\phantom{\rule{0.16em}{0ex}}^{10}\mathrm{B}$, and $^{16,18}\mathrm{O}$ projectiles on the same target at energies around the respective Coulomb barriers. Considering this data set, we report on optical model analyses based on the double-folding S\~ao Paulo potential. Within this approach, we study the sensitivity of the data fit to different models for the nuclear matter densities and to variations in the optical potential strengths.

Elastic scattering and transfer cross sections for the $^{7}\mathrm{Be}+^{9}\mathrm{Be}$ system have been measured at ${E}_{\mathrm{lab}}=23.1\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ using the $^{7}\mathrm{Be}$ radioactive secondary beam produced at Radioactive Ion Beams in Brazil facility at the University of S\~ao Paulo. The elastic scattering has been measured by detecting the $^{7}\mathrm{Be}$ scattered at forward angles in the laboratory system. The transfer reaction $^{9}\mathrm{Be}(^{7}\mathrm{Be},^{9}\mathrm{Be})^{7}\mathrm{Be}$ was identified by detecting the $^{9}\mathrm{Be}$ scattered at the same laboratory angles. The elastic angular distribution has been analyzed by optical model calculations using a Woods-Saxon form factor whose parameters have been varied to best reproduce the experimental data at forward angles. Coupled reaction channels calculations (CRC) have been performed to describe the transfer, considering the coupling to the transfer channel and including contributions to the ground state and to the first excited state of $^{7}\mathrm{Be}(1/2\ensuremath{-};429\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$) in the final state. The spectroscopic amplitudes used in the CRC calculation have been derived from shell-model calculations. Similar CRC calculations were applied to existing $^{9}\mathrm{Be}(p,t)^{7}\mathrm{Be}$ data to check the consistency of our results results for the ($^{7}\mathrm{Be},^{9}\mathrm{Be}$) transfer reaction.

A large yield of $\ensuremath{\alpha}$ particles produced in the $^{120}\mathrm{Sn}(^{6}\mathrm{He},\ensuremath{\alpha})$ reaction was measured at 20.3-, 22.2-, 22.4-, and 24.5-MeV bombarding energies. The $\ensuremath{\alpha}$ particles are distributed over a broad energy range in the vicinity and below the elastic scattering $^{6}\mathrm{He}$ peak. Energy integrated $\ensuremath{\alpha}$-particle cross sections have been obtained at ${\ensuremath{\theta}}_{\text{lab}}={36}^{\ensuremath{\circ}},{40}^{\ensuremath{\circ}}$, and ${60}^{\ensuremath{\circ}}$. The $\ensuremath{\alpha}$ energy distributions have been analyzed at a fixed laboratory angle $(\ensuremath{\approx}{60}^{\ensuremath{\circ}})$ in terms of the reaction $Q$ value, considering the $2n$-transfer reaction kinematics $^{120}\mathrm{Sn}(^{6}\mathrm{He},\ensuremath{\alpha})^{122}\mathrm{Sn}$. A kinematical analysis of the $Q$-value distribution shows that the recoil system $^{120}\mathrm{Sn}+2n$ is formed in highly excited states in the continuum, at increasing excitation energies as the bombarding energy increases. It is shown that by using Brink's formula, the excitation energy depends on the transferred angular momentum following a linear relation with the square of the angular momentum, indicating that some kind of dinuclear rotating system is formed after the reaction.

The 32S(3He,d)33Cl one-proton transfer reaction is a powerful tool to investigate the spectroscopy of low-lying states in the proton-rich 33Cl nucleus. However, the extraction of firm differential cross-section data at various angles to benchmark and constrain theoretical models is made challenging by the presence of competitive reactions on target contaminants. In this paper we report on a recent measurement using a new generation hodoscope of silicon detectors, capable to detect and identify emitted deuterons down to energies of the order of 2 MeV. The high angular segmentation of our hodoscope combined with a suitable target to control possible contaminants, allowed to unambiguously disentangle the contribution of various states in 33Cl, in particular the 2.352 MeV state lying just few tens of keV above the proton separation energy.

The 32S(3He,d)33Cl one-proton transfer reaction is a powerful tool to investigate the spectroscopy of low-lying states in the proton-rich 33Cl nucleus. However, the extraction of firm differential cross-section data at various angles, against which benchmarking theoretical models to correctly constrain the spectroscopy of 33Cl, is made challenging by the presence of competitive reaction products contaminating the detected energy spectra. We have recently measured the 32S(3He,d)33Cl reaction at 9.8 MeV incident energy by using a new generation hodoscope of silicon detectors, capable to detect and identify emitted deuterons down to energies of the order of 2 MeV. The high angular segmentation of our hodoscope allowed to unambiguously disentangle the contribution of one-proton transfer reactions in the ground state of 33Cl and in its 0.810 MeV, 2.352 MeV, 2.685 MeV, 2.846 MeV excited states from contaminant deuteron-emitting reactions. These data will be crucial to help to constrain Jπ and spectroscopic factor C 2 Sp values of low-lying 33Cl states, still ambiguous in the literature. The present status of the analysis is discussed in the paper.

We measured the $^{8}\mathrm{Li}(p,p)^{8}\mathrm{Li}$, $^{8}\mathrm{Li}(p,d)^{7}\mathrm{Li}$, and $^{8}\mathrm{Li}(p,\ensuremath{\alpha})^{5}\mathrm{He}$ reactions at low energies using the thick target inverse kinematics method, with a polyethylene ${[{\mathrm{CH}}_{2}]}_{n}$ target and a radioactive $^{8}\mathrm{Li}$ beam available at the Radioactive Ion Beams in Brazil facility of S\~ao Paulo. By measuring simultaneously several reaction channels $(p,p)$, $(p,d)$, and $(p,\ensuremath{\alpha})$, the still uncertain high-lying resonances of $^{9}\mathrm{Be}$, close to the proton threshold, can be studied and their parameters, such as energy, width, and spin parity can be more reliably determined. The experimental excitation functions of the reactions $^{8}\mathrm{Li}(p,p)^{8}\mathrm{Li}$, $^{8}\mathrm{Li}(p,d)^{7}\mathrm{Li}$, and $^{8}\mathrm{Li}(p,\ensuremath{\alpha})^{5}\mathrm{He}$ were analyzed using the $R$-matrix theory, which allows us to infer the properties of the resonances. Multichannel $R$-matrix analysis provides evidence for a significant clustering in the $(p,d)$ channel. The experimental data and the multichannel $R$-matrix analysis will be presented.

In this paper we discuss new experimental data on the one-proton transfer reaction 32S(3He, d)33Cl* at 9.68 MeV bombarding energy. An enriched 32S target and a high-granularity hodoscope were used to obtain data for proton transfer reactions to bound and unbound states in 33Cl. Angular distributions were interpreted by means of finite-range DWBA and coupled-channel calculations. The obtained spectroscopic factors have been compared with previous results reported in the literature and with shell model calculations.

A description of the RIBRAS (radioactive ion beams in Brasil) facility is presented and the last experimental developments in the system are reported.

The (p, p), (p, a) and (p, d) reactions on 8Li were measured at low energies. The experiment was performed using a thick [CH2]n target and a radioactive 8Li beam available at the RIBRAS facility of Sao Paulo . This experiment represents an upgrade of a previous experiment, where only the 8Li(p,a)5He cross section was measured. High lying resonances of 9Be, which are still uncertain, could be studied in this way. The detection of several reaction channels allows a reliable determination of the resonance parameters, such as energy, width and spin-parity. In the deuteron channel we could observe the same resonance decaying to d+7Ligs and to d+7Li∗. The properties of the resonances are determined by a R-matrix analysis, which provides evidence for a significant clustering as well in the (p, a) as in the (p, d) channels. The experimental data and the multi-channel R-matrix analysis will be presented.

We present $^{8}\mathrm{B}+^{27}\mathrm{Al}$ elastic scattering angular distributions for the proton-halo nucleus $^{8}\mathrm{B}$ at two energies above the Coulomb barrier, namely ${E}_{\mathrm{lab}}=15.3$ and 21.7 MeV. The experiments were performed in the Radioactive Ion Beams in Brasil facility (RIBRAS) in S\~ao Paulo, and in the TwinSol facility at the University of Notre Dame, USA. The angular distributions were measured in the angular range of 15--80 degrees. Optical model and continuum discretized coupled channels calculations were performed, and the total reaction cross sections were derived. A comparison of the $^{8}\mathrm{B}+^{27}\mathrm{Al}$ total reaction cross sections with similar systems including exotic, weakly bound, and tightly bound projectiles impinging on the same target is presented.

We present angular distributions of the He 6 + Ni 58 scattering measured at three bombarding energies above the Coulomb barrier: E lab = 12.2 MeV , 16.5 MeV , and 21.7 MeV . The angular distributions have been analysed in terms of three- and four-body Continuum-Discretized Coupled-Channels calculations considering the effect of the 6 He breakup. A behaviour in the cross section at large angles has been observed which was reproduced only by the four-body Continuum-Discretized Coupled-Channels calculation.

An overview of the experiments performed at RIBRAS over the last year is presented. Elastic scattering and breakup reactions induced by light exotic projectiles on different targets have been measured and some results are presented here for the 120Sn(6He, α) reaction. Resonant scattering experiments have been performed with 10Be and 12C secondary beams on a CH2 thick target and the well known 12C+p resonance was identified. A gamma-particle experiment using a new system of LYSO scintillators to detect gammas was done.

In this work we present an elastic scattering angular distribution for the 8Li+58Ni system measured at Elab = 26.1 MeV. The 8Li beam was produced in the Radioactive Ion Beams in Brasil (RIBRAS) facility using the 7Li primary beam delivered by the 8-UD Pelletron accelerator. The angular distribution covers the angular range from 20 to 85 degrees in the center of mass frame. The data have been analysed by optical model and coupled channels calculations, including couplings to low-lying states in 8Li and the spin-orbit interaction. Our results indicate that the inclusion of the spin-orbit interaction in the calculations is important to describe the data at backward angles.

The availability of radioactive beams provides new opportunities in nuclear physics [1]. On the one hand, they provide a probe of the nuclear structure in unusual conditions of excitation energy and isospin. Many experiments have been performed with beams such as 6He, 8He 11Li, 11Be, among others (see references in Ref. [1]). At energies near the Coulomb barrier or above, these experiments provide valuable information on the structure of exotic nuclei and on the dynamics of the nuclear reactions between them. On the other hand, recent experiments involving radioactive beams have been very successful in nuclear astrophysics, where many stellar scenarios involve short-lived nuclei [2].

Nuclear astrophysics is a relatively young science; it is about half a century old. It is a multidisciplinary subject, since it combines nuclear physics with astrophysics and observations in astronomy. It also addresses fundamental issues in astrobiology through the formation of elements, in particular those required for a carbon-based life. In this paper, a rapid overview of nucleosynthesis is given, mainly from the point of view of nuclear physics. A short historical introduction is followed by the definition of the relevant nuclear parameters, such as nuclear reaction cross sections, astrophysical S-factors, the energy range defined by the Gamow peak and reaction rates. The different astrophysical scenarios that are the sites of nucleosynthesis, and different processes, cycles and chains that are responsible for the building of complex nuclei from the elementary hydrogen nuclei are then briefly described.

The RIBRAS facility (Radioactive Ion Beams in Brasil) is installed in connection with the 8MV Pelletron tandem of the University of Sao Paulo Physics Institute. It consists of two superconducting solenoids which focalize light radioactive secondary beams of low energy, produced by transfer reactions. Recent experimental results include the elastic scattering and transfer reactions of 6He halo nucleus on 9Be, 27Al, 51V and 120Sn targets. The elastic scattering and transfer of 8Li and 7Be on several targets is also being studied. The transfer reaction 8Li(p,α)5He of astrophysical interest was also studied in the E c m = 0.2 – 2.5 MeV energy range.

A double superconducting solenoid system is installed at the Pelletron Laboratory of the Uni- versity of Sao Paulo, Brazil. This system allows the production of secondary beams of 8 Li, 6 He, 7 Be and others light exotic nuclei. The first results using this facility are presented.

A double superconducting solenoid system (RIBRAS) for the production of secondary light exotic nuclear beams was installed at the Sao Paulo Pelletron Laboratory of the University of Sao Paulo, Brazil. The two solenoids are presently operating in one of the beam lines of the 8 MV Tandem Accelerator. Secondary beams of 8 Li and 6 He were produced using a 7 Li primary beam and a production target of 9 Be. These beams were impinged on targets of 27 Al, 51 V and 197 Au and the scattered radioactive nuclei were detected in Si telescopes. Elastic scattering angular distributions were measured at several energies close and above the Coulomb barrier. The angular distributions were analysed with optical potentials and reaction cross sections were obtained from the optical model calculations.

The elastic scattering of the radioactive halo nucleus 6He on 27Al target was measured at four energies close to the Coulomb barrier using the RIBRAS (Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was used and its diffuseness and imaginary strength were adjusted to fit the elastic scattering angular distributions. Reaction cross-sections were extracted from the optical model fits. The reduced reaction cross-sections of 6He on 27Al are similar to those for stable, weakly bound projectiles as {6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al., 7 pages, 1 table, 3 figures

We present a quick description of RIBRAS (Radioactive Ion beams in Brazil), which is a superconducting double solenoid system, installed at the Pelletron Laboratory of the University of São Paulo and extends the capabilities of the original Pelletron Tandem Accelerator of 8MV terminal voltage (8UD) by producing secondary beams of unstable nuclei. The experimental program of the RIBRAS covers the study of elastic and inelastic scattering with the objective to study the interaction potential and the reaction mechanisms between weakly bound (RIB) and halo (6He and 8B) projectiles on light, medium and heavy mass targets. With highly purified beams, the study of resonant elastic scattering and resonant transfer reactions, using inverse kinematics and thick targets, have also been included in our recent experimental program., SCOPUS: cp.j, info:eu-repo/semantics/published

The energy-integrated reaction cross-sections of several neutron-rich nuclei ( 17−22 N, 19−24 O, 21−27 F, 23−30 Ne, 26−33 Na, 28−35 Mg, 31−38 Al, 33−40 Si, 36−42 P, 39−44 S, 42−45 Cl, 45,46 Ar), measured at intermediate energy (30–65 A MeV), via direct method, are presented. Silicon detectors have been used as the active target as well as for particles identification. The reduced strong absorption radii r 0 2 are extracted and compared to the data available from the literature. New measurements for 19 nuclei ( 27 F, 27,30 Ne, 33 Na, 28,34–35 Mg, 36−38 Al, 38−40 Si, 41−42 P, 42−44 S, 45 Cl) are revealed. From the study of the isospin dependence of the reduced strong absorption radius, a new quadratic parameterisation of the nuclear radii in the closed shell regions N = 8 and N = 28 , is proposed. According to this parameterisation, the proton/neutron rich nuclei skin effect is well described and a new anomalous structure: halo-structure or large deformation is suggested for 35 Mg and 44 S nuclei.

A double superconducting solenoid system is being installed at the Pelletron Laboratory of the University of S ao Paulo, Brazil. This system allows the production of secondary beams of light exotic nuclei like 8Li, 6He and others. The first results using this facility are presented.

Quantum tunnelling through a potential barrier ( such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom(1,2). A strong increase of the fusion probability has been observed for heavy deformed nuclei(3). In light exotic nuclei such as He-6, Li-11 and Be-11 ( termed 'halo' nuclei(4)), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial - it could induce a large enhancement of fusion(5), but alternatively the weak binding energy of the nuclei could inhibit the process(6). Other reaction channels known as direct processes ( usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus He-6 with a U-238 target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the ( large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.

Recent mass measurements of proton-rich nuclei close to the N=Z line were used for the calculation of the interaction strength δVpn between valence protons and neutrons. When compared with δVpn values calculated from mass values of the AME’95 mass tables, the breaking down of the SU(4) symmetry is verified at Z=32,33,34.

Transfer reactions are verified to be an important tool for the study of light unbound nuclei. We have studied the proton-rich unbound nuclei 15 F and 11 N, 10 N respectively through the 16 O( 14 N, 15 C) 15 F and 12 C( 14 N, 15 C) 11 N, 10 B( 14 N, 13 B) 11 N, 10 B( 14 N, 14 B) 10 N reactions. Resonance energies and width were obtained.

Resonances in 6Be and 5Li have been investigated by deuteron transfer reactions with radioactive ion beams, 2H(8B,α)6Be, 2H(7Be,α)5Li, respectively. There is an indication of a possible resonance at excitation energy of 9.6 MeV in 6Be, just below the 3He+3He threshold. The structure of the 6Li nucleus has been also investigated by the neutron transfer reaction 3He(7Li,α)6Li. In 6Li, a new resonance is observed at about 12.4 MeV in excitation energy and the presence of a resonance at 15.2 MeV is confirmed. The data are preliminary and a detailed analysis is in progress. The instalation of a Radioactive Ion Beam facility in Brazil (RIBRAS) is also reported.

Nuclear physics has been going through a major evolution over the last decade. The realization that one can investigate nuclei at extreme conditions such as high density, temperature, and angular momentum using several sophisticated experimental innovations opened up the possibility of extending this activity to the study of these systems when more neutrons or more protons are added. The so called exotic nuclei constitute a major research activity in Japan, France, USA, Canada, Germany and other countries. More laboratories are going through the process of re-direction of their experimental effort towards this activity. The nuclear physics community in Brasil has enthusiastically decided to join this endeavor to provide the Pelletron/LINAC complex with two superconducting solenoids which will permit the production of secondary beams of radioactive nuclei. A description of this facility and project RIBRAS follows.

Elastic angular distributions of the $^{6}\mathrm{He}$ + $^{9}\mathrm{Be}$ scattering at ${E}_{\mathrm{lab}}=16.2$ and 21.3 MeV have been analyzed in the context of the optical model. The projectile-target optical potential was calculated in a cluster model where the contributions from the fragment target $(\ensuremath{\alpha}{\ensuremath{-}}^{9}\mathrm{Be})$ and the dineutron target $(2n{\ensuremath{-}}^{9}\mathrm{Be})$ are separated and the latter was searched to reproduce the experimental data. The total reaction cross sections for the $^{6}\mathrm{He}$$\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}{}^{9}\mathrm{Be}$ system have been obtained, and the error bars have been estimated considering the spread between the present optical model and previous coupled channels and continuum discretized coupled-channels calculations. The cross sections have been reduced and compared in a systematics involving tightly bound, weakly bound, and the exotic $^{6}\mathrm{He}$ projectiles, all on $^{9}\mathrm{Be}$ target. An analysis of the enhancements observed in the total reaction cross section induced by $^{6}\mathrm{He}$ on light, medium mass, and heavy targets is presented.

RIBRAS (Radioactive Ion Beams in Brazil) is a facility installed at the Institute of Physics of the University of Sao Paulo (IFUSP), Brazil. The RIBRAS system consists of two superconducting solenoids and uses the “in-flight method” to produce radioactive ion beams using the primary beam provided by the 8UD Pelletron Tandem of IFUSP. The ion beams produced so far by RIBRAS are 6He, 8Li, 7Be, 10Be, 8B, 12B with intensities that can vary from 104 to 106 pps. Initially the experimental program covered the study of elastic and inelastic scattering with the objective to study the interaction potential and the reaction mechanisms between weakly bound (RIB) and halo (6He and 8B projectiles on light, medium and heavy mass targets. With highly purified beams, the study of resonant elastic scattering and resonant transfer reactions, using inverse kinematics and thick targets, has also been included in our experimental program. Also, transfer reactions of astrophysical interest and fusion reactions induced by halo nuclei are part of the near-future research program. Our recent results on elastic scattering, alpha-particle production and total reaction cross sections, as well as the resonant elastic and transfer reactions, are presented. Our plans for the near future are related to the installation of a new beam line and a cave for gamma-ray detection. We intend to place in operation a large area neutron detector available in our laboratory. The long-range plans could be the move of the RIBRAS system to the more energetic beam line of the LINAC post-accelerator (10MeV/nucleon primary beams) still in construction in our laboratory.

Elastic scattering angular distributions of the radioactive weakly bound $^{7}\mathrm{Be}$ on $^{27}\mathrm{Al}$ have been measured at energies near the Coulomb barrier. The interaction optical potential is investigated by using different potentials. Total reaction cross sections have also been obtained.

We present the results of the 8Li(p,α)5He and 8Li(p,p)8Li reactions measured at the RIBRAS (Radioactive Ion Beams in Brazil) system. The experiment was realized in inverse kinematics using a thick [CH2]n polyethylene target and an incident 8Li beam, produced by RIBRAS. Using the thick target method, the complete excitation function could be measured between Ecm = 0.2 - 2.1 MeV, which includes the Gamow peak energy region. The excitation function of the 8Li(p,α)5He reaction, populating resonances between 16.888 and 19.0 MeV in 9Be, was obtained[1] and the resonances were fitted using R-matrix calculations. This study shed light on spins, parities, partial widths and isospin values of high lying resonances in 9Be. The measurement of the resonant elastic scattering 8Li(p,p)8Li populating resonances in the same energy region can constrain the resonance parameters. Preliminary results of the elastic scattering are also presented. © Owned by the authors, published by EDP Sciences, 2014., SCOPUS: cp.p, info:eu-repo/semantics/published

We present the results of experiments using a 6 He beam on a 9 Be target at energies 7 − 9 times the Coulomb barrier. Angular distributions of the elastic, inelastic scattering (target breakup) and the a -particle production in the 6 He+ 9 Be collision have been analysed. Total reaction cross sections were obtained from the elastic scatteringanalyses and a considerable enhancement has been observed by comparing to stable systems.

Measurements of the p({sup 6}He,p) elastic scattering excitation function have been performed in the RIBRAS system using a {sup 6}He secondary beam and a CH{sub 2} polyethylene thick target. The motivation is to observe states of the compound nucleus {sup 7}Li in the excitation energy range of E{sub exc}{sup 7Li} = 10.8-11.8MeV, where the isobaric analog state of {sup 7}He ground state lies. Excitation functions have been obtained at three laboratory angles θ{sub lab} = 0°, 20°, and 25° which correspond to θ{sub c.m} = 180°, 140°, and 130°.

Elastic scattering measurements of 6He + 58Ni system have been performed at the laboratory energy of 21.7 MeV. The 6He secondary beam was produced by a transfer reaction 9Be (7Li, 6He) and impinged on 58Ni and 197Au targets, using the Radioactive Ion Beam (RIB) facility, RIBRAS, installed in the Pelletron Laboratory of the Institute of Physics of the University of Sao Paulo, Brazil. The elastic angular distribution was obtained in the angular range from 15° to 80° in the center of mass frame. Optical model calculations have been performed using a hybrid potential to fit the experimental data. The total reaction cross section was derived.

An extension of the time-integrated atomic decoupling technique to measure g -factors of (sub)nanosecond isomers and/or the magnetic hyperfine field induced by highly excited atomic electrons on nuclei recoiling into vacuum is discussed. A high average field B hf =1080 −175 +270 T and an average atomic spin J =2.7(2) is deduced using the known magnetic moment of a 4.05(7) μs isomer in 69 Ge. Such high magnetic fields allow g -factor measurements of (sub)nanosecond states. Ab initio calculations show that the combination of a high average magnetic hyperfine field and a high average atomic spin is only possible if a considerable fraction of the ions is in a metastable excited state.

The reaction cross section for the halo nucleus 6 He on hydrogen has been measured at 36 MeV/nucleon using the transmission method and a value of σ R =409±22 mb was obtained. A coherent analysis within a microscopic model of this result in conjunction with (p,p) and (p,n) angular distributions has allowed the interaction potential to be uniquely determined. This analysis also allowed the 6 He density distribution to be explored.

The spectroscopic quadrupole moment of the high-spin, high- K five-quasiparticle isomer (K(pi) = 35/2(-), T(1/2) = 750(80) ns, E(i) = 3349 keV) in (179)W has been determined using the level mixing spectroscopy method. A value Q(s) = 4.00(+0.83-1.06)e b was derived, which corresponds to an intrinsic quadrupole moment Q0 = 4.73(+0.98-1.25)e b and to a quadrupole deformation beta(2) = 0.185(+0.038-0.049). These values differ significantly from the deduced ground-state quadrupole moments and are in disagreement with the current theoretical predictions in this mass region.

Mass measurements of the N = Z nuclei 80Zr, 76Sr, 68Se were performed for the first time and a new measurement was obtained for 80Y, using the second cyclotron CSS2 of GANIL as a high-resolution spectrometer. Ions around N = Z were produced by fusion-evaporation in the inverse 58Ni (4.32 MeV A) + 24Mg and 12C reactions. New masses were measured by a time-of-flight method, with a precision of 2 · 10-6, by using well-known masses as references. Study of the double binding energy difference δV np is then performed leading to a strong N = Z Wigner effect around N = Z = 40. Knowledge of new masses in this region also plays a crucial role in the modelling of the astrophysical rp process.

The mass-measurement programme at GANIL aims to measure the masses of heavy nuclei close to the N = Z line which is the ideal region to study neutron-proton pairing. An original direct time-of-flight mass-measurement method was developed at GANIL which uses the CSS2 cyclotron as a high-resolution spectrometer. The masses of ions of A = 68, 76, 80 and 100 have been measured with a precision of a few 10-6. Mass measurements will be performed with the new CIME cyclotron of SPIRAL using a similar method based on the measurement of the phase of the accelerated ions for different radio-frequencies. A recently approved experiment will help develop this new technique and aims to measure the mass of 31 Ar radioactive nuclei with a precision of 10-6.