Experimental probe for the production of ${}^{97}\mathrm{Ru}$ from the ${}^7\mathrm{Li}+{}^{93}\mathrm{Nb}$ reaction: A study of precompound emissions

Background: Interaction of weakly bound heavy ions with an intermediate or heavy target is not yet understood completely due to the scarcity of experimental data. In order to develop a clear understanding of breakup fusion or preequilibrium emission even in the low energy range, 3–10 MeV/nucleon, more experimental investigations are necessary.

Purpose: We aim to study the reaction mechanisms involved in the weakly bound heavy-ion induced reaction ${}^7\mathrm{Li}+{}^{93}\mathrm{Nb}$ at low energies by measuring the production cross sections of the residual radionuclides.

Method: Natural niobium (${}^{93}\mathrm{Nb}$) foil, backed by an aluminum (Al) catcher, arranged in a stack was bombarded by ${}^7\mathrm{Li}$ ions of 20–45 MeV energy. Activity of the residues produced in each ${}^{93}\mathrm{Nb}$ target was measured by off line $\gamma$-ray spectrometry after the end of bombardment (EOB) and cross sections were calculated. Experimental cross sections were compared with those computed using compound and precompound models.

Results: In general, measured excitation functions of all residues produced in the ${}^7\mathrm{Li}+{}^{93}\mathrm{Nb}$ reaction showed good agreement with the model calculations based on the Hauser-Feshbach formalism and the exciton model for compound and precompound processes, respectively. Significant preequilibrium emission of neutrons was observed at the relatively high energy tail of the excitation function of ${}^{97}\mathrm{Ru}$.

Conclusions: Preequilibrium processes played an important role in the enhancement of the cross section in the $xn$ reaction channel over the compound reaction mechanism at higher energies for the ${}^7\mathrm{Li}+{}^{93}\mathrm{Nb}$ reaction. Additionally, indirect evidence of incomplete or breakup fusion was also perceived.

Figure 1

$\gamma$-ray spectrum of ${}^7\mathrm{Li}$ activated niobium foil collected 34 minutes after the EOB.

Figure 2

Comparison of experimental (symbols) excitation functions of ${}^{97}\mathrm{Ru}$ from the ${}^7\mathrm{Li}+{}^{93}\mathrm{Nb}$ reaction and those obtained from theoretical (curves) estimation from pace4, alice91, and empire3.2.

Figure 3

Comparison of experimental (symbols) and calculated (curves) excitation functions for production of ${}^{95}\mathrm{Ru}$.

Figure 4

Comparison of experimental (symbols) and calculated (curves) excitation functions for production of ${}^{96}\mathrm{Tc}$.

Figure 5

Comparison of experimental (symbols) and calculated (curves) excitation functions for production of ${}^{95}\mathrm{Tc}$.

Figure 6

Comparison of experimental (symbols) and calculated (curves) excitation functions for production of ${}^{93m}\mathrm{Mo}$.