Effects of unconventional breakup modes on incomplete fusion of weakly bound nuclei

The incomplete fusion dynamics of ${}^6\mathrm{Li}+{}^{209}\mathrm{Bi}$ collisions at energies above the Coulomb barrier is investigated. The classical dynamical model implemented in the platypus code is used to understand and quantify the impact of both ${}^6\mathrm{Li}$ resonance states and transfer-triggered breakup modes (involving short-lived projectile-like nuclei such as ${}^8\mathrm{Be}$ and ${}^5\mathrm{Li}$) on the formation of incomplete fusion products. Model calculations explain the experimental incomplete-fusion excitation function fairly well, indicating that (i) delayed direct breakup of ${}^6\mathrm{Li}$ reduces the incomplete fusion cross sections and (ii) the neutron-stripping channel practically determines those cross sections.

Figure 1

(a) Incomplete-fusion excitation function when direct breakup of ${}^6\mathrm{Li}$ into $\alpha$ and deuteron happens in collisions with the ${}^{209}\mathrm{Bi}$ target: prompt breakup (solid line), delayed breakup (dashed line). (b) The same but for the no-capture breakup excitation curve.

Figure 2

$\alpha$ and deuteron contributions to the incomplete-fusion excitation function for prompt direct breakup of ${}^6\mathrm{Li}$ in collisions with ${}^{209}\mathrm{Bi}$.

Figure 3

(a) Relative kinetic-energy distributions for $\alpha \text{−}{}^{209}\mathrm{Bi}$ and $d\text{−}{}^{209}\mathrm{Bi}$ immediately following the prompt direct breakup of ${}^6\mathrm{Li}$ in collisions with ${}^{209}\mathrm{Bi}$ at $E_{c.m.}=50.5$ MeV. (b) The same but the energy is measured relative to the height of the Coulomb barriers between each cluster and the ${}^{209}\mathrm{Bi}$ target. The arrows denote the partition of the ${}^6\mathrm{Li}$ incident energy between these clusters according to their masses.

Figure 4

Experimental incomplete-fusion cross-sections for ${}^6\mathrm{Li}+{}^{209}\mathrm{Bi}$ [24] are compared with platypus calculations at above-barrier (arrow) energies. Direct breakup as well as transfer-triggered breakup channels are included. (a) For delayed direct breakup of ${}^6\mathrm{Li}$, delayed breakup of ${}^8\mathrm{Be}$ after $d$ pickup, and delayed breakup of ${}^5\mathrm{Li}$ after $n$ stripping. (b) The same but for prompt breakup processes.