Measuring Barriers to Fusion

Abstract

The experimental extraction of detailed barrier distributions has brought a significant advance in the study of the fusion of heavy nuclei, and indeed in the entire heavy-ion reaction process. A quantitative understanding of the entrancechannel effects induced by target and projectile structure has emerged, based on recent high-precision measurements of fusion excitation functions. These distributions show clearly whether the experimental data are good enough to give the information required. They are also the functions best suited to the theoretical interpretation of the reaction dynamics-often presenting an unambiguous "fingerprint" of the target and projectile structure. We are now at the stage where we can start to exploit the insights gained in order to understand properties of the compound nucleus created: its spin distribution and evaporation residues, perhaps its possible shapes, and, in the case of heavy systems, its subsequent fission.

Examining the role of transfer coupling in sub-barrier fusion ofTi46,50+Sn124

“…As mentioned above, the Q-values for neutron transfer are negative for both reactions. The subbarrier fusion enhancement for 46 40 Ca+ 124 Sn [7] and 46 Ti+ 124 Sn were obtained by taking the second derivative of the product of the cross section and energy using the point difference formula [29]. The barrier distributions are compared in Fig.…”

Fusion and breakup in the reactions of 6,7Li and 9Be

“…An important question here is: does the breakup process influence fusion reactions in a similar way as the inelastic process, which leads to subbarrier enhancement [ 1] of fusion cross sections over predictions for a single barrier? In addressing this question, measurements with weakly bound stable nuclei, such as 9 Be, 6 Li, and 7 Li, have been proved to be useful [ 2,3,4].…”

Sub-barrier fusion enhancement with radioactive134Te

“…Heavy-ion fusion below the Coulomb barrier presents the opportunity to study the quantum tunneling of many-body systems [1,2]. For relatively light systems (Z 1 Z 2 250), the fusion probability below the barrier can be described well using the single barrier penetration model (BPM) [2,3].…”

“…For relatively light systems (Z 1 Z 2 250), the fusion probability below the barrier can be described well using the single barrier penetration model (BPM) [2,3]. However, for heavier systems dramatic enhancements beyond the BPM were observed in the fusion probability below the barrier [1][2][3][4]. This was discovered to be associated with the coupling of additional degrees of freedom, such as vibrational and rotational excitations, which modify the single Coulomb barrier producing a distribution of barriers [1,2].…”

“…However, for heavier systems dramatic enhancements beyond the BPM were observed in the fusion probability below the barrier [1][2][3][4]. This was discovered to be associated with the coupling of additional degrees of freedom, such as vibrational and rotational excitations, which modify the single Coulomb barrier producing a distribution of barriers [1,2]. Coupledchannel calculations provide a powerful tool to calculate the fusion excitation functions with the inclusion of couplings to inelastic excitations and/or rotational bands [2,5].…”