Effect of neutron excess in the entrance channel on the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ system: An experimental study relevant to incomplete-fusion dynamics

The incomplete fusion dynamics in the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ system at energies above the Coulomb barrier has been investigated. The experimentally measured cross sections have been compared with the theoretical predictions of the statistical model code pace4. To examine the effect of entrance channel parameters on the onset and strength of incomplete fusion, relative contributions of complete and incomplete fusion have been deduced from the analysis of measured excitation functions. The contribution of incomplete fusion deduced from the analysis of excitation functions has been studied in terms of various entrance channel parameters, namely, entrance channel mass asymmetry (${\mu }_A$) of interacting projectile and target combination, Coulomb factor ($Z_P{Z}_T$), ground state $\alpha \text{−}Q$ value of the reaction, and neutron skin thickness of target nuclei. It has been found that the probability of incomplete fusion depends strongly on entrance channel parameters. Further, the incomplete fusion contribution for the ${}^{18}\mathrm{O}$ projectile with two excess neutrons is noticed to be relatively larger as compared to ${}^{16}\mathrm{O}$. This may be due to the larger probability of breakup for the ${}^{18}\mathrm{O}$ projectile resulting in rather weak binding forces as compared to ${}^{16}\mathrm{O}$. The existence of incomplete fusion below critical angular momentum (${\ell }_{\mathrm{crit}}$), i.e., $\ell ⩽{\ell }_{\mathrm{crit}}$, has also been observed for the studied system.

Figure 1

Typical $\gamma$-ray energy spectrum obtained from the interaction of the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ system at $E_{\mathrm{lab}}=92.2$ MeV energy. Some of the identified $\gamma$-ray peaks have been assigned to their respective evaporation residues populated via CF and/or ICF channels.

Figure 2

(a) Experimentally measured EFs of evaporation residue ${}^{108}\mathrm{In}(3n$) along with pace4 calculations ($K=8$, 10, and 12). (b) Experimentally measured EFs of evaporation residues ${}^{107}\mathrm{In}(4n$) and ${}^{106}\mathrm{In}(5n$) along with pace4 calculations ($K=12$).

Figure 3

(a) Experimentally measured EFs of all $pxn$ ($x=3$ and 5) channels. (b) Sum of all CF channels along with pace4 calculations ($K=12$).

Figure 4

CF cross section as a function of $1/E_{\mathrm{lab}}$ found to reproduce the Coulomb barrier for the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ system. The dashed line through the data point is achieved by a best-fitting producer on the data point.

Figure 5

Experimentally measured EFs ${}^{105}\mathrm{Ag}$, ${}^{104}\mathrm{Ag}$, and ${}^{103}\mathrm{Ag}$ panels [(a)–(c)] are compared with PACE4 predictions (K = 12). Hollow symbol represents the measured cumulative cross section.

Figure 6

Experimentally measured EFs ${}^{102}\mathrm{Ag}$ and ${}^{101}\mathrm{Ag}$ are compared with PACE4 predictions (K = 12).

Figure 7

Experimentally measured EFs ${}^{100}\mathrm{Pd}$, ${}^{100}\mathrm{Rh}$, ${}^{99}\mathrm{Rh}$, ${}^{101}\mathrm{Tc}$, ${}^{96}\mathrm{Tc}$, and ${}^{95}\mathrm{Tc}$ are compared with pace4 predictions ($K=12$).

Figure 8

The total fusion cross section ${\sigma }_{TF}$ along with the sum of complete fusion and incomplete fusion cross section ($\mathrm{\Sigma }{\sigma }_{CF}$ and $\mathrm{\Sigma }{\sigma }_{ICF}$), and in the inset the probability of incomplete fusion, are plotted as a function of incident projectile energy.

Figure 9

The comparison of deduced $F_{ICF}(\%)$ as a function of normalized relative velocity ($V_{rel}/c$) for ${}^{18}\mathrm{O}$ projectile on different targets. For references and details see text.

Figure 10

Comparison of deduced $F_{ICF}(\%)$ of the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ system with earlier studied systems as a function of entrance channel mass asymmetry (${\mu }_A$) at same relative velocity ($V_{\mathrm{rel}}=0.053c$). The lines drawn are just to guide the eye. For references and details see text.

Figure 11

The $F_{ICF}(\%)$ deduced from the present system along with those obtained for earlier studied systems as a function of Coulomb factor ($Z_P{Z}_T$) at the same relative velocity ($V_{\mathrm{rel}}=0.053c$). The color lines drawn through the data points are just to guide the eyes. For references and details see text.

Figure 12

The variation of incomplete fusion fraction with neutron skin thickness ($t_N$) at relative velocity, $V_{\mathrm{rel}}=0.053c$. For references and details see text.

Figure 13

Comparison of deduced $F_{ICF}(\%)$ as a function of normalized projectile energy for ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ and ${}^{16}\mathrm{O}+{}^{93}\mathrm{Nb}$ systems.

Figure 14

Fusion $\ell$ distributions for the ${}^{18}\mathrm{O}+{}^{93}\mathrm{Nb}$ and ${}^{16}\mathrm{O}+{}^{93}\mathrm{Nb}$ [49] systems calculated using the ccfull code [58] and by incorporating the coupled-channel calculations at $\approx 99.20$ MeV energy.