Transfer/Breakup Channel Couplings in Sub-barrier Fusion Reactions

Abstract

With the recent availability of state-of-the-art radioactive ion beams, there has been a renew interest in the investigation of nuclear reactions with heavy ions near the Coulomb barrier. The role of inelastic and transfer channel couplings in fusion reactions induced by stable heavy ions can be revisited. Detailed analysis of recent experimental fusion cross sections by using standard coupled-channel calculations is first discussed. Multi-neutron transfer effects are introduced in the fusion process below the Coulomb barrier by analyzing 32 S+ 90,96 Zr as benchmark reactions. The enhancement of fusion cross sections for 32 S+ 96 Zr is well reproduced at sub-barrier energies by NTFus code calculations including the coupling of the neutrontransfer channels following the Zagrebaev semi-classical model. Similar effects for 40 Ca+ 90 Zr and 40 Ca+ 96 Zr fusion excitation functions are found. The breakup coupling in both the elastic scattering and in the fusion process induced by weakly bound stable projectiles is also shown to be crucial. In the second part of this work, full coupled-channel calculations of the fusion excitation functions are performed by using the breakup coupling for the more neutron-rich reaction and for the more weakly bound projectiles. We clearly demonstrate that Continuum-Discretized Coupled-Channel calculations are capable to reproduce the fusion enhancement from the breakup coupling in 6 Li+ 59 Co.

Examining the enhancement of sub-barrier fusion cross sections by neutron transfer with positiveQ values

“…This method is not fully microscopic, but it takes into account approximately the main effects of neutron rearrangement with positive Q values. The ECC model with neutron rearrangement has been already successfully used in several papers [10][11][12][13][14] to reproduce and predict cross sections for sub-barrier fusion reactions of stable nuclei.…”

“…The mechanism of sequential fusion was proposed in [10], in which an additional sub-barrier fusion enhancement owing to neutron rearrangement with positive Q values at the approaching stage was described for the first time. The corresponding semiclassical model of this process was developed and successfully used for the predictions [10,11] and description of several fusion reactions [12][13][14].…”

Analysis of fusion dynamics of colliding systems involving stable, loosely bound and halo nuclei

“…This idea leads to the exploration of a number of reactions involving weakly bound colliding systems but the enhancement or suppression of fusion cross-section due to breakup effects is still at a controversial stage and further investigations are needed for its clarifications. In the fusion of weakly bound nuclei, one can believe that the breakup process has strong impacts on the energy dependence of low energy fusion cross-sections [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In this regard, the present article analyzed the fusion of Li Sm, + reactions [10,11,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] within the view of the energy dependent Woods-Saxon potential model (EDWSP model) and coupled channel approach.…”

Role of projectile breakup effects and intrinsic degrees of freedom on fusion dynamics

“…The various interesting features of heavy fusion reactions like fusion enhancement and fusion suppression are associated with the nuclear structure of participating nuclei. It has been recognized that the fusion mechanism of tightly bound nuclei in the close vicinity of the Coulomb barrier is strongly influenced by the intrinsic structure degrees of freedom of the colliding pairs [1][2][3][4][5][6][7]. For stable nuclei, the coupling of the relative motion of the colliding nuclei to their nuclear structure degrees of freedom, like collective surface vibrational states (spherical nuclei), rotational states (deformed nuclei), nucleon (multi-nucleon) transfer channels etc., eliminates the discrepancies between experimental fusion data and the expectations of the one-dimensional barrier penetration model [8][9][10][11][12][13].…”