Study of reactions induced by 6He on 9Be

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

Mass Measurements of Neutron-Deficient Yb Isotopes and Nuclear Structure at the Extreme Proton-Rich Side of the N=82 Shell

International audienceHigh-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN’s multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of Yb150,153 and the excitation energy of Ybm151 were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h11/2-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculation

The Li-8(p, alpha)He-5 reaction at low energies, and Be-9 spectroscopy around the proton threshold

We present a direct measurement of the low-energy Li-8(p, alpha)He-5 cross section, using a radioactive Li-8 beam impinging on a thick target. With four beam energies, we cover the energy range between E-c.m. = 0.2 and 2.1 MeV. An R-matrix analysis of the data is performed and suggests the existence of two broad overlapping resonances (5/2(+) at E-c.m. = 1.69 MeV and 7/2(+) at E-c.m. = 1.76 MeV). At low energies our data are sensitive to the properties of a subthreshold state (E-x = 16.67 MeV) and of two resonances above threshold. These resonances were observed in previous experiments. The R-matrix fit confirms spin assignments, and provides partial widths. We propose a new Li-8(p, alpha)He-5 reaction rate and briefly discuss its influence in nuclear astrophysics. DOI: 10.1103/PhysRevC.86.064321Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2003/10099-2, 2004/07379-6, 2008/09341-7]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Comissao de Aperfeicoamento do Ensino Superior (CAPES)Comissao de Aperfeicoamento do Ensino Superior (CAPES

Proton-Induced Reactions on 8Li at Low Energies and Spectroscopy of 9Be at High Excitation Energies

Reações induzidas por prótons são importantes no estudo do consumo de 8Li em alguns cenários astrofísicos. Neste trabalho, as seções de choque para as reações 8Li(p,p), 8Li(p,α) e 8Li(p,d) foram medidas em cinemática inversa entre Ecm=0.7 e 2.2 MeV. Foi usado um feixe de 8Li de alta pureza selecionado pelo Sistema RIBRAS no Laboratório Pelletron (IF-USP), São Paulo, que colidia com um alvo grosso de polietileno ((CH2)n, 7.7(8) mg/cm2), um plástico rico em prótons. Os produtos de reação foram medidos por um telescópio formado por detectores de barreira de superfície de silício posicionados em um ângulo dianteiro. As funções de excitação medidas foram analisadas através da metodologia de matriz-R e puderam fornecer informações sobre ressonâncias pouco conhecidas do núcleo composto 9Be a altas energias de excitação. A importância de outros canais de decaimento e consequências das reações estudadas na nucleossíntese também são discutidas.Proton-induced reactions are important in the study of the destruction of 8Li in some astrophysical scenarios. In this work, the cross sections for the reactions 8Li(p,p), 8Li(p,α) and 8Li(p,d) were measured in inverse kinematics between Ecm = 0.7 and 2.2 MeV. A highly pure 8Li beam selected by RIBRAS System in the Pelletron Laboratory (IF-USP), São Paulo, was used impinging on a thick polyethylene target ((CH2)n , 7.7(8) mg/cm2), a proton-rich plastic. The reaction products were detected by a telescope formed by silicon surfasse barrier detectors placed at a foward angle. The measured excitation functions were analysed through the R-matrix methodology and could provide information about poorly known high-lying resonances of the 9Be compound nucleus. The importance of other decay channels and the consequences of the studied reactions on nucleosynthesis are also discussed

Dawning of nuclear magicity in N = 32 seen through precision mass spectrometry

In the early days of nuclear science, physicists were astounded that specific "magic" combinations of neutrons or protons within nuclei seemed to bind together more tightly than other combinations. This phenomenon was related to the formation of shell structures in nuclei. More recently, nuclear shells were observed to emerge or vanish as we inspect nuclei further from stability. The structural evolution of these changing shells has been the object of intense experimental investigation, and their behavior has become a standard ruler to benchmark theoretical predictions. In this work, we investigated the emergence of shell effects in systems with 32 neutrons (N = 32) using mass spectrometry techniques. Evidence for "magicity" was observed in potassium (with 19 protons, or Z = 19), calcium (Z = 20) and scandium (Z = 21), but not in vanadium (Z = 23) and higher-Z elements. In between, the picture at titanium (Z = 22) was unclear. We produced neutron-rich isotopes of titanium and vanadium through nuclear reactions at the ISAC facility and measured their atomic masses at the TITAN facility, in the TRIUMF Laboratory in Vancouver. These measurements were performed with the newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer at TITAN facility and were substantiated by independent measurements from the Penning trap mass spectrometer. The atomic masses of ⁵²⁻⁵⁵Ti and ⁵²⁻⁵⁵V isotopes were measured with high precision, right at the expected emergence of N = 32 shell effects. Our results conclusively establish the existence of weak shell effects in titanium and confirm their absence in vanadium. Calculations of the N = 32 nuclear shell are within reach of the so-called ab initio theories. In these, complex atomic nuclei are described theoretically from fundamental principles, by applying principles of Quantum Chromodynamics to many-body quantum methods. Our data were compared with a few state-of-the-art ab initio calculations which, despite very successfully describing the N = 32 shell effects in Ca and Sc isotopes, overpredict its strength in Ti and erroneously assign V as its point of appearance. We hope the deficiencies revealed by our work will guide the development of the next generation of ab initio theories.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

High-precision mass measurement of neutron-rich 96Kr

International audienceWhile the nuclear deformation in the region around Z = 40 and N = 60 has been studied in great detail, the possible onset of nuclear deformation in the isotopic chain of krypton (Z = 36) is still a subject of controversy. Here, we present a high-precision mass measurement of the neutron-rich nuclide $^{96}$Kr, as measured by the Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) at TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN). A statistical method, based on a hyper-exponentially modified Gaussian, has been employed to model the data. As such, the uncertainty introduced by overlapping peaks from beam contaminants was reduced and the mass excess of $^{96}$Kr determined to be -53097(57)keV. The capability of the method has been confirmed with measurements of the stable isotopic pair $^{40}$Ar/$^{40}$Ca, in which a relative accuracy Δm/m of 3.5 ⋅ 10$^{− 8}$ and a mass resolving power of more than 400000 were achieved

First Experiment with the Double Solenoid RIBRAS System.

A description of the double solenoid system (RIBRAS) operating since 2004 in one of the beam lines of the Pelletron Laboratory of the Institute of Physics of the University of São Paulo is presented. The recent installation of the secondary scattering chamber after the second solenoid is reported and the first experiment in RIBRAS using both solenoids is described.FAPESPCNP

(7,9,10)Be elastic scattering and total reaction cross sections on a (12)C target

Elastic scattering angular distributions for (7)Be, (9)Be, and (10)Be isotopes on (12)C target were measured at laboratory energies of 18.8, 26.0, and 23.2 MeV, respectively. The analysis was performed in terms of optical model potentials using Woods-Saxon and double-folding form factors. Also, continuum discretized coupled-channels calculations were performed for (7)Be and (9)Be + (12)C systems to infer the role of breakup in the elastic scattering. For the (10)Be + (12)C system, bound states coupled-channels calculations were considered. Moreover, total reaction cross sections were deduced from the elastic scattering analysis and compared with published data on other weakly and tightly bound projectiles elastically scattered on the (12)C target, as a function of energy.Conselho Nacional de Pesquisa e Desenvolvimento (CNPq)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP