Statistical-model analyses of heavy-ion-induced fusion reaction products

Abstract

Results are presented of statistical/rotating liquid drop model analyses of fusion reaction products produced by heavy-ion reactions on medium mass target nuclei. Statistical fission parameters $\frac{a_f}{a_{\nu }}$ and $B_f$ are deduced from analyses of fission and evaporation residue excitation functions. The validity of approximations often made in fusion reaction product analyses regarding the treatment of multiple-chance fission competition by evaporation residues in reactions at high bombarding energies are compared with experimental results. The experimental limits of evaporation residue survival are found to be adequately reproduced by the statistical/rotating liquid drop model using the statistical fission parameters deduced from the excitation function analyses. Using these parameters, calculations are performed of evaporation residue angular momentum distributions and their moments. The influence upon these distributions of fission competition, particle emission, and the moment of inertia (yrast slope) is illustrated, and calculated results are compared with those inferred from $\gamma$-ray multiplicity measurements. The statistical fission parameters required to reproduce the fission and evaporation residue excitation functions are given by: $\frac{a_f}{a_{\nu }}=1.00\mathrm{} \mathrm{to} 1.04$ and $B_f=0.51\mathrm{} \mathrm{to} 0.65$. The expected existence of thermal and deformation effects, as well as other reaction processes which could affect the parameters, is discussed. Since these aspects have not been incorporated into the formulation of the present model, it is emphasized that the deduced $\frac{a_f}{a_{\nu }}$ and $B_f$ values should be regarded as effective statistical fission parameters.