Unraveling the Reaction Mechanisms Leading to Partial Fusion of Weakly Bound Nuclei

Abstract

Collisions between complex nuclei may give rise to their total or partial fusion. The latter case is found experimentally to gain importance when one of the colliding nuclei is weakly bound. It has been commonly assumed that the partial fusion mechanism is a two-step process, whose first step is the dissociation of the weakly bound nucleus, followed by the capture of one of the fragments. To assess this interpretation, we present the first implementation of the three-body model of inclusive breakup proposed in the 1980s by Austern et al. [Phys. Rep. 154, 125 (1987)] that accounts for both the direct, one-step, partial fusion and the two-step mechanism proceeding via the projectile continuum states. Contrary to the widely assumed picture, we find that, at least for the investigated cases, the partial fusion is largely dominated by the direct capture from the projectile ground-state.

Role of continuum in nuclear direct reactions with one-neutron halo nuclei: A one-dimensional model

“…Including also the projectile continuum improves the result (CC (3) ), thus showing that in a perturbation picture the transfer is not a one-step process, but it is reached through successive steps involving the continuum. Multistep processes in direct reactions are traditionally inferred by CDCC calculations, and, as we have seen in the previous section, continuum-continuum couplings play a crucial role [41,43,44].…”

The Hussein–McVoy formula for inclusive breakup revisited

“…By contrast, in Eqs. (18) and (19), the presence of the V post operator will tend to emphasize small b − x separations and hence one requires only an approximate three-body wavefunction accurate within that range. This can be achieved, for instance, expanding 3B(+) in terms of b − x eigenstates, as done in the CDCC method [11], or in terms of Weinberg states [17].…”

“…This can be achieved, for instance, expanding 3B(+) in terms of b − x eigenstates, as done in the CDCC method [11], or in terms of Weinberg states [17]. The implementation of the method with CDCC wavefunctions is numerically challenging and the first calculation of this kind was only recently reported [18].…”

Unraveling the reaction mechanism for large alpha production and incomplete fusion in reactions involving weakly bound stable nuclei

“…While the (two-step) process of breakup followed by capture of the "free" complementary fragment (x) is widely believed to be responsible, a few recent studies suggest the dominant role of (direct) cluster stripping. To achieve an unambiguous experimental discrimination between these two processes, a coincidence measurement between the outgoing α particles and γ rays from the heavy residues has been performed for the 7 Li(α+triton)+ 93 Nb system. Proper choice of kinematical conditions allowed for the first time a significant population of the region accessible only to the direct triton stripping process and not to breakup followed by the capture of the "free" triton (from the three-body continuum).…”

“…In many light nuclei, α clustering is responsible for the weak binding of α + x cluster configurations. A large α-particle yield compared to that of the complementary fragment (x) is observed in nuclear reactions involving such nuclei, e.g., 6,7 Li and 7,9 Be, indicating that it cannot arise solely due to simple breakup of the weakly-bound projectile in the field of the target Email address: sanat@barc.gov.in (S. K. Pandit) nucleus. Capture/transfer of the complementary fragment/cluster, also sometimes referred to as incomplete fusion (ICF), has also been observed with similar magnitudes in these reactions.…”