${}^7\mathrm{Li}$-induced reaction on ${}^{\mathrm{nat}}\mathrm{Mo}$: A study of complete versus incomplete fusion

Background: Several investigations on the complete-incomplete fusion (CF-ICF) dynamics of $\alpha$-cluster well-bound nuclei have been contemplated above the Coulomb barrier $(\sim 4$–7 MeV/nucleon) in recent years. It is therefore expected to observe significant ICF over CF in the reactions induced by a weakly bound $\alpha$-cluster nucleus at slightly above the barrier.

Purpose: Study of the CF-ICF dynamics by measuring the populated residues in the weakly bound ${}^7\mathrm{Li}+{}^{\text{nat}}\mathrm{Mo}$ system at energies slightly above the Coulomb barrier to well above it.

Method: In order to investigate CF-ICF in the loosely bound system, ${}^7\mathrm{Li}$ beam was bombarded on the ${}^{\text{nat}}\mathrm{Mo}$ foils, separated by the aluminium (Al) catcher foils alternatively, within $\sim 3$–6.5 MeV/nucleon. Evaporation residues produced in each foil were identified by the off-line $\gamma$-ray spectrometry. Measured cross section data of the residues were compared with the theoretical model calculations based on the equilibrium (EQ) and pre-equilibrium (PEQ) reaction mechanisms.

Results: The experimental cross section of ${}^{101\text{m},100,99\text{m},97}\mathrm{Rh},{}^{97,95}\mathrm{Ru},{}^{99\text{m},96,95,94,93\text{m}+\text{g}}\mathrm{Tc}$, and ${}^{\text{93m}}\mathrm{Mo}$ residues measured at various projectile energies were satisfactorily reproduced by the simplified coupled channel approach in comparison to single barrier penetration model calculation. Significant cross section enhancement in the $\alpha$-emitting channels was observed compared to EQ and PEQ model calculations throughout observed energy region. The ICF process over CF was analyzed by comparing with EMPIRE. The increment of the incomplete fusion fraction was observed with increasing projectile energies.

Conclusions: Theoretical model calculations reveal that the compound reaction mechanism is the major contributor to the production of residues in ${}^7\mathrm{Li}+{}^{\text{nat}}\mathrm{Mo}$ reaction. Theoretical evaluations substantiate the contribution of ICF over the CF in $\alpha$-emitting channels. EMPIRE estimations shed light on its predictive capability of cross sections of the residues from the heavy-ion induced reactions.

Figure 1

A $\gamma$-ray spectrum of the ${}^7\mathrm{Li}+{}^{\text{nat}}\mathrm{Mo}$ reaction at 42.8 MeV energy after 1.2 h of EOB (characteristic $\gamma$-ray peaks are shown in keV).

Figure 2

Excitation functions of the ${}^{\text{101m,100,99m,97}}\mathrm{Rh}$ radionuclide populated through $xn$ channels are compared with EMPIRE and PACE calculations.

Figure 3

Excitation functions of the ${}^{\text{97,95}}\mathrm{Ru}$ populated through $pxn$ channels are compared with EMPIRE and PACE calculations.

Figure 4

Excitation functions of the ${}^{\text{99m,96,95,94}}\mathrm{Tc}$ residues are compared with EMPIRE and PACE calculations.

Figure 5

Excitation functions of the ${}^{\text{93m+g}}\mathrm{Tc},{}^{\text{93m}}\mathrm{Mo}$ residues are compared with EMPIRE and PACE calculations.

Figure 6

Sum of the $xn,pxn$, and $\alpha xn$ channels cross sections are compared with the EMPIRE and PACE in (a) and (b), respectively. (c) shows total fusion (TF), complete fusion (CF), and incomplete fusion (ICF) with incident energy. (d) represents variation of incomplete fusion fraction with increasing projectile energy.