Estruturas Nucleares e Reações

V. Guimarães, J. Lubian, J. J. Kolata, E. F. Aguilera, M. Assunção and V. Morcelle

The European Physical Journal A. December 2018, 54:223

Abstract

We have surveyed a series of elastic scattering measurements from the literature involving tightly bound (9Li, 10Be, 12C, 16O, 19F), weakly bound (6Li, 7Li, 8Li, 8He, 9Be, 17F), and exotic (6He and 11Li) nuclei on a 208Pb target at energies close to the Coulomb barrier. The corresponding data were then converted and analyzed in terms of the interaction distance, where critical-interaction and strong-absorption distances were extracted. Larger values were obtained for the exotic 6He and 11Li nuclei, as compared with both weakly bound and tightly bound projectiles. The influence of long-range nuclear interactions and Coulomb dipole polarizability are discussed. A correlation between the critical interaction distance and binding energy for a given configuration is observed.

10.1140/epja/i2018-12662-7

E. Leistenschneider, A. Lépine-Szily, M. A. G. Alvarez, D. R. Mendes, Jr., R. Lichtenthäler, V. A. P. Aguiar, M. Assunção, R. Pampa Condori, U. U. da Silva, P. N. de Faria, N. Deshmukh, J. G. Duarte, L. R. Gasques, V. Guimarães, E. L. A. Macchione, M. C. Morais, V. Morcelle, K. C. C. Pires, V. B. Scarduelli, G. Scotton, J. M. B. Shorto, and V. A. B. Zagatto

Phys. Rev. C 98, 064601

Abstract

We measured the 8Li(p, p)8Li, 8Li(p, d)7Li, and 8Li(p, α)5He reactions at low energies using the thick target inverse kinematics method, with a polyethylene [CH2]n target and a radioactive 8Li beam available at the Radioactive Ion Beams in Brazil facility of São Paulo. By measuring simultaneously several reaction channels (p, p), (p, d), and (p, α), the still uncertain high-lying resonances of 9Be, 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 8Li(p, p)8Li, 8Li(p, d)7Li, and 8Li(p, α)5He 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.

10.1103/PhysRevC.98.064601

R. Linares, M. J. Ermamatov, J. Lubian, F. Cappuzzello, D. Carbone, E. N. Cardozo, M. Cavallaro, J. L. Ferreira, A. Foti, A. Gargano, B. Paes, G. Santagati, and V. A. B. Zagatto

Phys. Rev. C 98, 054615

ABSTRACT

Background: Recently, a systematic exploration of two-neutron transfer induced by the (18O,16O) 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 (18O,17O) reaction on 16O,28Si, and 64Ni 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 18O+16O and the 18O+28O systems, we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the 18O+64Ni 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 18O+16O and 18O+64Ni systems.

10.1103/PhysRevC.98.054615

L. F. Canto, R. Donangelo, M. S. Hussein, P. Lotti, J. Lubian, and J. Rangel

Phys. Rev. C 98, 044617 – Publicado em 22 October 2018

ABSTRACT

We carefully compare the one-dimensional Wentzel, Kramers, Brillouin barrier tunneling model, and the one-channel Schrödinger equation with a complex optical potential calculation of heavy-ion fusion, for a light and a heavy system. It is found that the major difference between the two approaches occurs around the critical energy, above which the effective potential for the grazing angular momentum ceases to exhibit a pocket. The value of this critical energy is shown to be strongly dependent on the nuclear potential at short distances, on the inner region of the Coulomb barrier, and this dependence is much more important for heavy systems. Therefore the nuclear fusion process is expected to provide information on the nuclear potential in this region. We compare calculations with available data to show that the results are consistent with this expectation.

DOI:10.1103/PhysRevC.98.044617

Added, M. C. Morais, and P. R. S. Gomes

Phys. Rev. C 98, 044614 – Published 17 October 2018

ABSTRACT

A precise quasielastic excitation function for the 18O+63Cu system has been measured at energies around the Coulomb barrier at θLAB=161∘. The corresponding quasielastic barrier distribution has been derived. Two-neutron-, one-proton-, and α-transfer-excitation functions have also been measured at the same energies and angle. Coupled reaction channels calculations were performed to describe the experimental data. Large-scale shell-model calculations were performed to derive most of the spectroscopic amplitudes. No surface imaginary potential was necessary for the interaction potential because almost all relevant reaction channels were explicitly included in the calculation. The theoretical results were compared to the experimental quasielastic barrier distribution and a very good agreement was achieved. The comparison of the coupled reaction channel calculations and data has put in evidence several important details of the reaction mechanism of the 18O+63Cu system. The collectivity of the 63Cu nucleus has important contribution to the reaction mechanism of this system, mainly due to its first 5/2+ and 7/2+ states. It was also observed a striking influence on the reaction dynamics of the 18O(2+) state, the two-neutron transfer and the reorientation of the target ground-state spin. The best agreement to data was achieved when the nuclear matter diffuseness for the 18O was assumed equal to 0.60 fm, value that we have derived in a previous paper and that is 10% greater than the 16O diffuseness. Another significant result was that the two-neutron transfer process is much more relevant than the one-neutron-transfer process, which suggests that the pairing correlation could play an important role in the transfer process of this system.

DOI:10.1103/PhysRevC.98.044614

E. N. Cardozo, M. J. Ermamatov, J. L. Ferreira, B. Paes, M. Sinha and J. Lubian

Eur. Phys. J. A (2018) 54: 150

ABSTRACT

In this paper, we analyze the one-neutron pick-up from the 55Mn target when it is bombarded by 17MeV deuteron, by performing coupled reaction channel (CRC) calculations. Spectroscopic amplitudes for CRC calculations, and structural information such as reduced B(E2) transition probabilities, quadrupole, and magnetic momenta, are obtained from shell-model calculations using the fp-kb3 interaction. The calculated structure quantities are in good agreement with the available experimental data for both target and ejectile. Analyses of angular distributions show the relevance of microscopic information for the description of the higher excited states of 54Mn .

DOI:10.1140/epja/i2018-12587-1