Scattering of6He at energies around the Coulomb barrier

Nuclear Physics A, 2008

The elastic scattering of 6 He on 208 Pb has been measured at laboratory energies of 14, 16, 18 and 22 MeV. These data were analyzed using phenomenological Woods-Saxon form factors and optical model calculations. A semiclassical polarization potential was used to study the effect of the Coulomb dipole polarizability. Evidence for long range absorption, partially arising from Coulomb dipole polarizability, is reported. The energy variation of the optical potential was found to be consistent with the dispersion relations which connect the real and imaginary parts of the potential.

2012

G. Marquínez-Durán, A.M. Sánchez Benítez, I. Martel R. Berjillos, J. Dueñas, V.V. Parkar, L. Acosta K. Rusek, M.A.G. Álvarez, J. Gómez-Camacho M.J.G. Borge , C. Cruz , M. Cubero , V. Pesudo , O. Tengblad A. Chbihi, J.P. Fernández-García, B. Fernández-Martínez J.A. Labrador, A.H. Ziad, J.L. Flores, N. Keeley L. Standylo, I. Strojek, M. Marques, M. Mazzocco A. Pakou, N. Patronis, D. Pierroutsakou, R. Silvestri R. Raabe, N. Soic, R. Wolski

Recent developments aimed to understand the observed features arising in the scattering of the Borromean nucleus 6 He on heavy targets are discussed and compared with recent data for 6 He+ 208 Pb measured at the RIB facility at Louvain-la-Neuve at energies around the Coulomb barrier. The analysis of the elastic scattering data in terms of the optical model, reveals the presence of a long range absorption mechanism, that manifests in the form of a large value of the imaginary diffuseness parameter. The elastic data have been also compared with three-body CDCC calculations, based on a di-neutron model of 6 He, and four-body CDCC calculations, based on a more realistic three-body model of this nucleus. Finally, the angular and energy distribution of α particles emitted at backward angles are discussed and compared with different theoretical approaches. We find that these α particles are produced mainly by a two-neutron transfer mechanism to very excited states in the residual nucleus.

AIP Conference Proceedings, 2009

Recent developments aimed to understand the observed features arising in the scattering of the Borromean nucleus 6 He on heavy targets are discussed and compared with recent data for 6 He+ 208 Pb measured at the RIB facility at Louvain-la-Neuve at energies around the Coulomb barrier. The analysis of the elastic scattering data in terms of the optical model, reveals the presence of a long range absorption mechanism, that manifests in the form of a large value of the imaginary diffuseness parameter. The elastic data have been also compared with three-body CDCC calculations, based on a di-neutron model of 6 He, and four-body CDCC calculations, based on a more realistic three-body model of this nucleus. Finally, the angular and energy distribution of α particles emitted at backward angles are discussed and compared with different theoretical approaches. We find that these α particles are produced mainly by a two-neutron transfer mechanism to very excited states in the residual nucleus.

Physical Review C, 2001

The interaction of 6 He with 209 Bi has been studied over a range of energies well below the nominal Coulomb barrier. A 4 He group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 5 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneouslymeasured elastic scattering angular distribution.

Nuclear Physics A, 2006

Quasi-elastic scattering of 6 He at E lab =27 MeV from 197 Au has been measured in the angular range of 6 • − 72 • in the laboratory system employing LEDA and LAMP detection systems. These data, along previously analysed data of 6 He + 208 Pb at the same energy, are analysed using Optical Model calculations. The role of Coulomb dipole polarizability has been investigated. Large imaginary diffuseness parameters are required to fit the data. This result is an evidence for long range absorption mechanisms in 6 He induced reactions.

Nuclear Physics A, 2003

Elastic scattering of 6 He at E lab = 27 MeV with 208 Pb has been measured in the angular range of 6 • -72 • in the laboratory system employing LEDA and LAMP detection systems. Optical Model calculations have been performed using dynamic polarisation potential. The role of Coulomb dipole polarisability has been investigated. Large values of the imaginary diffuseness parameter are required in order to fit the data.

Physical Review C, 2019

Optical model analyses of recent 8 He + 208 Pb elastic scattering data for incident energies of 16 and 22 MeV, together with existing data for 6 He + 208 Pb at the same energies, reveal a significant difference in the behavior of the imaginary part of the optical potential for the two isotopes as the incident energy is reduced below the Coulomb barrier. While the strength of the 6 He imaginary potential reduces as the incident energy is reduced below the barrier, as is the case for most heavy ions, that for 8 He remains constant within uncertainties and may even increase. Similar behavior was observed for the 6 Li and 7 Li + 208 Pb optical potentials [Nucl. Phys. A 571, 326 (1994)], with the strength of the 6 Li imaginary potential appearing to increase as the incident energy is reduced below the Coulomb barrier while that for 7 Li reduces. However, the explanation for this difference in behavior put forward in that work, viz. the increased importance of breakup for 6 Li as the incident energy is reduced towards the Coulomb barrier, later supported explicitly by calculations [Phys. Lett. B 427, 1 (1998)], does not hold for the He isotopes since it is the 8 He optical potential that behaves in a similar fashion to that of 6 Li in spite of 8 He having the higher breakup threshold of the two He isotopes. We conclude that the difference is due to the influence of 3n and 4n stripping on the 8 He scattering, reactions which cannot take place for 6 He projectiles.

Acta Physica Polonica B, 2016

The structure and dynamics of 8 He have been studied through the collision process with a 208 Pb target at energies of 22 and 16 MeV, above and below the Coulomb barrier, respectively. The energy and angular distributions of the elastically scattered 8 He and the 6,4 He fragments were measured. In this paper, we discuss the method used to determine the effective position of the beam spot on the reaction target and the scattering and solid angles of each pixel of the detector array.

The exotic nucleus 8 He is investigated by means of the measurement of the angular distributions of the elastic channel and the 6 He and 4 He fragment yields produced in the collision with a 208 Pb target at two energies around the Coulomb barrier, 16 and 22 MeV. The experiment was performed at the GANIL-SPIRAL facility, with the aim of extracting information about the structure of 8 He and the relevant reaction mechanisms. In this contribution, details of the experimental setup and preliminary data on elastic cross sections are reported.