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

TL;DR

This study clarifies that direct cluster stripping, rather than breakup and capture, is the main process behind large alpha particle production and incomplete fusion in reactions involving weakly-bound nuclei, using coincidence measurements.

Contribution

It provides the first experimental discrimination between breakup and direct cluster stripping, confirming the dominance of the latter in alpha production for the studied system.

Findings

Direct cluster stripping dominates alpha production.

Coincidence measurements distinguish reaction mechanisms.

Cluster-transfer calculations support experimental results.

Abstract

The origin of the large $\alpha$ particle production and incomplete fusion in reactions involving weakly-bound $\alpha$+$x$ cluster nuclei still remains unresolved. 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 $\alpha$ particles and $\gamma$ rays from the heavy residues has been performed for the $^7$Li($\alpha$+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). This result, also supported by a cluster-transfer calculation, clearly establishes the dominance of the direct cluster-stripping mechanism in the large alpha production.