Near barrier fusion excitation function of ${}^6\mathrm{Li}+{}^{208}\mathrm{Pb}$

The fusion cross sections of ${}_{}{}^6\mathrm{Li}+{}_{}{}^{208}\mathrm{Pb}$ system at energies near the barrier have been measured by means of the evaporation residue method and have been calculated in terms of the coupled-channels model, taking into account single and double phonon octupole excitations of ${}^{208}\mathrm{Pb}$ and the $3^{+}$ rotational state of ${}^6\mathrm{Li}$. By comparing the experimental results with the theoretical calculations and with the fusion cross section of ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$, in which no breakup happens, we conclude that the fusion cross sections of ${}^6\mathrm{Li}+{}^{208}\mathrm{Pb}$ are suppressed at above-barrier energies due to the effects of ${}^6\mathrm{Li}$ breakup, but below the barrier, the effects of breakup are not clear.

Figure 1

A typical one-dimensional total energy spectrum from online analysis.

Figure 2

A spectrum from offline measurements, with three peaks corresponding to 5.305, 5.867, and $7.450\text{MeV}$, respectively. The last two groups are of $\alpha$ decay from ${}^{211}\mathrm{At}$, the other one is from ${}^{210}\mathrm{Po}$ which is a daughter nucleus of ${}^{210}\mathrm{At}$.

Figure 3

A typical spectrum of the elastic peaks of ${}^6\mathrm{Li}$ on the ${}^{208}\mathrm{Pb}$ target and on the ${}^{64}\mathrm{Cu}$ backing.

Figure 4

The measured cross sections of At isotopes. The solid lines are the results of PACE2 calculations.

Figure 5

Total fusion cross sections for ${}^6\mathrm{Li}+{}^{208}\mathrm{Pb}$. The solid squares are results of this experiment. The solid and dashed lines correspond to the coupled-channels code CCFULL [21, 23] calculations taking into account single and double phonon $3^{-}$ excitations in ${}^{208}\mathrm{Pb}$ and the spectroscopic quadrupole moment of the ${}^6\mathrm{Li}$ nucleus, with and without coupling to its $3^{+}$ unbound excited state, respectively. The dotted line corresponds to the one-dimensional barrier penetration model and the thick solid line corresponds to the full-couplings calculation, multiplied by the constant suppression factor 0.66. For the parameters used in the calculations, see text.

Figure 6

A comparison of the fusion cross sections and those of breakup for the system of ${}^6\mathrm{Li}+{}^{208}\mathrm{Pb}$. The open symbols are the data of breakup quoted from Refs. 1, 2, 28, 29. The solid and dashed lines are the predictions of CCFULL and CDCC [2] for fusion and breakup reactions, respectively.

Figure 7

The reduced fusion excitation functions of three similar systems ${}^9\mathrm{Be}+{}^{208}\mathrm{Pb}$ [13], ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$ [30], and ${}^6\mathrm{Li}+{}^{208}\mathrm{Pb}$.