Fusion studies in ${}^{35,37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions via evaporation residue cross section measurements

The fusion evaporation residue (ER) excitation function has been measured for ${}^{35,37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions at energies above the Coulomb barrier. The measurements were performed using the HYbrid Recoil mass Analyzer at IUAC, New Delhi. Comparable ER cross sections have been observed in both reactions and there is no isotopic dependence. Measured ER cross sections were compared with theoretical calculations employing the dinuclear system model at projectile and target nuclei interaction and statistical model for the deexcitation of the formed compound nucleus. Larger ER cross sections at the complete deexcitation cascade of the formed compound nucleus are noticed in both reactions at higher excitation energies $(E^{*}>80 \mathrm{MeV})$ over the calculated results. Fusion probability varies from $95\%$ to $40\%$ in the excitation energy range of the study. No appreciable difference in the fusion probability is noticed in the two reactions. Comparison of our results with other reactions populating ${}^{216}\mathrm{Th}$ shows a very strong entrance channel dependence.

Figure 1

The $\mathrm{\Delta }E$ versus $\text{ToF}$ spectrum at 225.7 MeV beam energy at the center of the target for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reaction. ERs are shown inside the elliptical gate.

Figure 2

Panel (a) shows the $\mathrm{\Delta }E$ versus $\text{ToF}$ spectrum at 225.7 MeV beam energy for the ${}^{35}\mathrm{Cl}$ beam with blank target. Panel (b) shows the two-dimensional spectra for background runs.

Figure 3

Comparison of the measured ER cross sections for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ and ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions as a function of the excitation energies.

Figure 4

The fission barrier for the compound nuclei ${}^{216}\mathrm{Th}$ and ${}^{218}\mathrm{Th}$ which are formed in the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ and ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions, respectively.

Figure 5

Partial fusion [(a) and (b)], fast fission [(c) and (d)], and quasifission [(e) and (f)] cross sections (in units of $\mathrm{mb}/\hslash$) for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ and ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions, respectively, as a function of excitation energy and angular momentum.

Figure 6

PES (in MeV) calculated for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reaction populating ${}^{216}\mathrm{Th}$ is shown as a function of the distance ($R$) between the interacting nuclei and charge numbers ($Z$) of the fragments. The arrow (a) shows the capture path, (b) the fusion path, and (c) is one of the QF paths.

Figure 7

The driving potentials calculated for dinuclear systems formed in the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ and ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions for orbital angular momentum $\ell =60\hslash$ as a function of the fragment $Z$.

Figure 8

Total ER cross sections are compared with the calculations (solid black line) for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reaction. Calculated capture, fusion, quasifission, fast fission, and $\sum xn$ channel cross sections are also shown in the same figure, as a function of excitation energy.

Figure 9

Same as in Fig. 8, but for the ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reaction.

Figure 10

Capture, fusion, quasifission, and fast fission cross sections for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ and ${}^{37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions, as a function of excitation energy.

Figure 11

$P_{\mathrm{CN}}$ for the ${}^{35,37}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reactions as a function of excitation energy.

Figure 12

The comparison of the calculated capture and fusion cross sections for the ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ reaction with ${}^{40}\mathrm{Ar}+{}^{176}\mathrm{Hf}$, ${}^{86}\mathrm{Kr}+{}^{130}\mathrm{Xe}$, and ${}^{124}\mathrm{Sn}+{}^{92}\mathrm{Zr}$ reactions [31], as a function of the energy in the center-of-mass frame normalized by the respective Coulomb barrier.