Probing the fusion ofLi7withNi64at near-barrier energies

Abstract

Background: The stable isotopes of Li, $^{6}\text{Li}$ and $^{7}\text{Li}$, have two-body cluster structures of $\ensuremath{\alpha}+d$ and $\ensuremath{\alpha}+t$ with $\ensuremath{\alpha}$-separation energies or breakup thresholds at 1.47 and 2.47 MeV, respectively. The weak binding of these projectiles introduces several new reaction channels not usually observed in the case of strongly bound projectiles. The impact of these breakup or breakup-like reaction channels on fusion, the dominant reaction process at near-barrier energies, with different target masses is of current interest.Purpose: Our purpose is to explore the fusion, at above and below the Coulmb barrier, of $^{7}\text{Li}$ with $^{64}\text{Ni}$ target in order to understand the effect of breakup or breakup-like processes with medium-mass target in comparison with $^{6}\text{Li}$, which has a lower breakup threshold.Measurement: The total fusion (TF) excitation of the weakly bound projectile $^{7}\text{Li}$ with the medium-mass target $^{64}\text{Ni}$ has been measured at the near-barrier energies (0.8 to $2 {V}_{B}$). The measurement was performed using the online characteristic $\ensuremath{\gamma}$-ray detection method. The complete fusion (CF) excitation function for the system was obtained using the $xn$-evaporation channels with the help of statistical model predictions.Results: At the above barrier energies CF cross sections exhibit an average suppression of about 6.5% compared to the one-dimensional barrier penetration model (1DBPM) predictions, while the model describes the measured TF cross section well. But below the barrier, both TF and CF show enhancements compared to 1DBPM predictions. Unlike $^{6}\text{Li}$, enhancement of CF for $^{7}\text{Li}$ could not be explained by inelastic coupling alone.Conclusion: Whereas the ${\ensuremath{\sigma}}_{\mathrm{TF}}$ cross sections are almost the same for both the systems in the above barrier region, the suppression of ${\ensuremath{\sigma}}_{\mathrm{CF}}$ at above the barrier is less for the $^{7}\text{Li}+^{64}\text{Ni}$ system than for the $^{6}\text{Li}+^{64}\text{Ni}$ system. Also direct cluster transfer has been identified as the probable source for producing large enhancement in TF cross sections.