Measurement of excitation functions of evaporation residues in the ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ reaction and investigation of the dependence of incomplete fusion dynamics on entrance channel parameters

Excitation functions for the 11 evaporation residues populated through complete and/or incomplete fusion in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system at low projectile energies $\approx 3-7\mathrm{MeV}/\mathrm{nucleon}$ have been measured. Recoil catcher activation technique followed by offline $\gamma$-ray spectrometry has been employed. Some of the evaporation residues are found to have contributions from precursor decays. The precursor contributions have been separated out from the measured cumulative cross-sections of evaporation residues. Independent cross-sections are compared with statistical model code PACE-4 predictions. The evaporation residues produced through $xn$ and pxn channels are found to be well reproduced with the PACE-4 predictions after subtraction of precursor decay contributions. A substantial enhancement in the measured excitation functions over their theoretical predictions for the evaporation residues produced in $\alpha$-emitting channels has been observed, which is attributed to the presence of incomplete fusion of projectile with target at these low energies. The present study shows that the incomplete fusion and the break-up probability of the incident ${}^{16}\mathrm{O}$ into $\alpha$ clusters (i.e., break-up of ${}^{16}\mathrm{O}$ into ${}^{12}\mathrm{C}+\alpha$ and/or ${}^8\mathrm{Be}+{}^8\mathrm{Be}$) increases with projectile energy. The present data suggests that the deformation of target is highlighting the important role to affect the ICF reactions independently with different projectiles. The comparison of the present study with literature data also shows that the ICF probability depends on various entrance channel parameters, namely, projectile energy, entrance channel mass-asymmetry, $\alpha \text{−}Q$ value, Coulomb factor $\left(Z_{\mathrm{P}}{Z}_{\mathrm{T}}\right)$, deformation parameter (${\beta }_2$), and their combinations. Moreover, the combined parameters $Z_{\mathrm{P}}{Z}_{\mathrm{T}}·{\beta }_2$ and ${\mu }_{\mathrm{EC}}^{\mathrm{AS}}·{\beta }_2$ are not found suitable to explain whole ICF characteristics, particularly for spherical and slightly deformed targets. On the other hand, the combined parameter $Z_{\mathrm{P}}{Z}_{\mathrm{T}}·{\mu }_{\mathrm{EC}}^{\mathrm{AS}}$ has been found to explain more precisely the ICF dynamics as compared to other single and combined entrance channel parameters.

Figure 1

Typical $\gamma$-ray spectrum showing $\gamma$ lines of different evaporation residues populated via CF and/or ICF reaction in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system at beam energy 99.7 MeV.

Figure 2

Excitation functions for the ERs ${}^{137\mathrm{m},\mathrm{g}}\mathrm{Ce}\left(3n\right)$, ${}^{135}\mathrm{Ce}\left(5n\right)$, ${}^{133\mathrm{m},\mathrm{g}}\mathrm{Ce}\left(7n\right)$, and ${}^{133}\mathrm{La}\left(p6n\right)$ produced in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system. Solid and hollow symbols represent measured data. The dash, solid, and dash-dotted lines correspond to the theoretical predictions of PACE-4 code for $K=8$, 10, 12, respectively.

Figure 3

Sum of all measured EFs of $xn$ and $pxn$ emission channels $\left({\sigma }_{\mathrm{SUM}(xn+pxn)}^{\mathrm{meas}}\right)$ populated in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system along with PACE-4 predictions $\left({\sigma }_{\mathrm{SUM}(xn+pxn)}^{\mathrm{PACE}-4}\right)$ at $K=10$.

Figure 4

Excitation functions for ERs ${}^{133\mathrm{m}}\mathrm{Ba}\left(\alpha 3n\right)$, ${}^{131\mathrm{m},\mathrm{g}}\mathrm{Ba}\left(\alpha 5n\right)$, ${}^{129\mathrm{m},\mathrm{g}}\mathrm{Ba}\left(\alpha 7n\right)$, ${}^{135\mathrm{m}}\mathrm{Cs}\left(\alpha p\right)$, and ${}^{132}\mathrm{Cs}\left(\alpha p3n\right)$ produced in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system. Solid and hollow symbols represent the measured data. The solid line corresponds to theoretical predictions of the PACE-4 code at $K=10$.

Figure 5

Excitation functions for ERs ${}^{131\mathrm{m}}\mathrm{Xe}\left(2\alpha n\right)$ and ${}^{131}\mathrm{I}\left(2\alpha p\right)$ produced in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system. Solid and hollow circles represent the measured data. The solid line corresponds to theoretical predictions of the PACE-4 code at $K=10$.

Figure 6

Sum of all measured EFs of $\alpha xn+\alpha pxn+2\alpha xn+2\alpha pxn$ channels $\left({\sigma }_{\mathrm{SUM}(\alpha xn+\alpha pxn+2\alpha xn+2\alpha pxn)}^{\mathrm{meas}}\right)$ populated in ${}^{16}\mathrm{O}+{}^{124}\mathrm{Sn}$ system along with PACE-4 predictions $\left({\sigma }_{\mathrm{SUM}(\alpha xn+\alpha pxn+2\alpha xn+2\alpha pxn)}^{\mathrm{PACE}-4}\right)$ at $K=10$.

Figure 7

The incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ for various projectile target systems as function of entrance channel mass asymmetry ${\mu }_{\mathrm{EC}}^{\mathrm{AS}}$ at a constant value $\left({\ell }_{max}\text{−}{\ell }_{\mathrm{crit}}\right)/{\ell }_{max}=0.12$. The dotted lines are drawn to represent the incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ data for different projectiles.

Figure 8

Incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ of various systems as a function of Coulomb factor $\left(Z_{\mathrm{P}}{Z}_{\mathrm{T}}\right)$ at constant value $\left({\ell }_{max}\text{−}{\ell }_{\mathrm{crit}}\right)/{\ell }_{max}=0.12$. Dotted lines are drawn to represent the incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ data.

Figure 9

Incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ of various systems as a function of deformation parameter (${\beta }_2$) of target at constant value $\left({\ell }_{max}\text{−}{\ell }_{\mathrm{crit}}\right)/{\ell }_{max}=0.12$. Dash dotted curves are drawn to represent $F_{\mathrm{ICF}}$ data for different projectiles.

Figure 10

Comparison of incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ as a function of $\left({\ell }_{max}\text{−}{\ell }_{\mathrm{crit}}\right)/{\ell }_{max}$ for different projectile target systems, with the same deformation parameter $\left({\beta }_2\right)$.

Figure 11

Incomplete fusion fraction $\left(F_{\mathrm{ICF}}\right)$ as a function of (a) $Z_{\mathrm{P}}{Z}_{\mathrm{T}}·{\beta }_2$ (b)${\mu }_{EC}^{AS}·{\beta }_2$ and (c) $Z_{\mathrm{P}}{Z}_{\mathrm{T}}·{\mu }_{EC}^{AS}$ for different projectile target systems at a constant value of $\left({\ell }_{max}\text{−}{\ell }_{\mathrm{crit}}\right)/{\ell }_{max}=0.12$.