Fusion and direct reactions for the system6He+64Zn at and below the Coulomb barrier

Abstract

Fusion and transfer + breakup channels have been studied in the collision induced by the two-neutron-halo 6 He on a 64 Zn target at energies from below to above the Coulomb barrier. For comparison, the reaction induced by the stable isotope 4 He on the same target has been studied. The fusion cross section has been measured by using an activation technique, detecting off-line the delayed x-ray activity following the electron capture decay of the evaporation residues. New measurements of the 4 He + 64 Zn fusion cross section at sub-barrier energies have been performed in order to cover the same energy range of the 6 He + 64 Zn fusion cross section and to compare the excitation functions for the two systems down to the lowest energy data point measured for 6 He. From the new comparison a sub-barrier fusion enhancement has been observed in the 6 He case with respect to the 4 He one whereas no effect on the 6 He fusion cross section has been seen at energies above the barrier. It has been concluded that such enhancement seems to be due to the diffuse halo structure properties of the 6 He nucleus. Moreover, the reactions induced by 6 He have shown a strong yield of α particles coming from direct processes.

Breakup and n -transfer effects on the fusion reactions Li6,7+Sn120,Fisichella1, Shotter2, Фігуера3 et al. 2017Phys. Rev. CSelf Cite19030View full textAdd to dashboardCite

“…This will enable several activation measurements at different energies to be simultaneously undertaken with a fixed beam energy. This has already been done in previous similar experiments [40,42,[44][45][46][47][48][49][50], thus reducing the beam time needed for the measurement. However, using a stack introduces problems which can complicate the interpretation of the activation results.…”

“…The same technique has been used successfully to measure the fusion excitation functions of the systems 6,7 Li, 4,6 He + 64 Zn [40][41][42][43]. The experimental technique involves two separate stages.…”

Coupled-Channel Effects in Collisions Between Heavy Ions Near the Coulomb Barrier

“…For reactions induced by weakly bound nuclei [16,17,25,26,27,28,39,40,41] and exotic nuclei [18,19,20,21,22,38,42,43,44,45,46], the breakup channel is open and plays a key role in the fusion process near the Coulomb barrier similarly to the transfer-channel coupling described in the previous section. It is therefore appropriate to use the Continuum-Discretized Coupled-Channel (CDCC) approach [47,48,49,50] to describe the influence of the breakup channel in both the elastic scattering and the fusion process at sub-barrier energies.…”

“…Either the standard WoodsSaxon form of the nuclear potential or a proximity potential [37] can be chosen. The code is also able to predict fusion cross sections for reactions induced by halo projectiles [30]; for instance 6 He + 64 Zn [22,38]. In the following, only comparisons for 32 S + 90 Zr and 32 S + 96 Zr are discussed.…”

“…Recent studies with Radioactive Ion Beams (RIB) indicate that the halo nature of 6,8 He [18,19,20,21,22], for instance, does not enhance the fusion probability as anticipated. Rather the prominent role of one-and two-neutron transfers in 6,8 He induced fusion reactions was definitively demonstrated.…”