Above-barrier fusion enhancement of proton-halo systems

Abstract

Previously reported data for fusion of the 8 B + ( 58 Ni, 28 Si) systems are critically reviewed. New α particle data from the fusion of 8 B + 58 Ni also are reported, but the paper is mostly based on using realistic calculations of well established codes to reanalyze the previous data. The influence of breakup protons on the evaporation proton measurements for the heavier system is found to be small at all energies except for the lowest one measured, and corrections are made for this process. Possible model dependencies in the deduced fusion cross sections are investigated using three different evaporation codes. The data sets for the 58 Ni and 28 Si targets are shown to be consistent with each other and with fusion enhancement up to energies that are greater than the Coulomb barrier V b (E c.m. < ∼ V b + 1.5×hω). This limit corresponds to 6.2 MeV above the barrier for the 58 Ni target. An important difference with the behaviour of neutron-halo systems is thus confirmed.PACS numbers: 25.60. Pj ,

Classical dynamical modelling of near-barrier breakup

“…Indeed, many works have noted a correlation between the direct breakup threshold and the degree of fusion suppression [19,20]. This correlation is apparent not only for weakly-bound stable nuclides such as 6,7 Li, 9 Be and 6 He, but also for more well-bound nuclides such as 10,11 B, 12,13 C and 16 O. So on the face of it we might conclude that direct breakup causes fusion suppression.…”

“…At this conference seen talks experimental measurements of reactions of 7 Be (Mazzocco), 8 B (Kolata [11]), and the halo nucleus 11 Be (Pesudo [12]), in addition to time-dependent Hartree-Fock calculations for exotic calcium isotopes (Vo-Phouc [13]). Innovative technical developments were also presented, such as new methods for extraction of fusion excitation functions with stacked targets, which will soon be utilized in experiments with exotic beams (Di Pietro [14,15]).…”

Near and sub-barrier reactions of 8B

“…See Ref. [19] for a further discussion). In addition, the sum of the 58 Ni total fusion cross section plus the direct breakup yield equals the experimentally-measured total reaction cross section (Fig.…”

“…[12,13], the total fusion cross section from Refs. [17,19], and the breakup cross section from Refs. [14,15] and also the CDCC calculation [16].…”

“…However, it was suggested that the evaporation proton yield might have been contaminated by direct breakup protons even at backward angles [18]. Therefore, an intensive study of this possibility was carried out [19]. The calculations of Ref.…”