Precompound evaporation analyses of excitation functions for (α,xn) reactions

Abstract

Calculated ($\ensuremath{\alpha},x\mathrm{n}$) excitation functions ($x=1 \mathrm{to} 4$) for $^{233,234,235}\mathrm{U}$ and $^{237}\mathrm{Np}$ targets, for incident $^{4}\mathrm{He}$ energies to 45 MeV, have been compared with experimental results. Calculations used experimental fission barriers with single particle ratios which were deduced by fitting experimentally deduced fission probabilities at excitations up to 12 MeV. Standard precompound parameters used for fitting spectra of nucleon-induced reactions were used, changing only the initial exciton number to four, appropriate for $\ensuremath{\alpha}$-induced reactions. Agreement with experimental results was good to excellent, without the need of multiple precompound decay, nor of variation of precompound decay parameters from those required for nonfissile systems.