Alpha Particles and Protons Emitted in the Bombardment ofAu197andBi209byC12,N14, andO16Projectiles

Abstract

Angular distributions, energy spectra, and absolute cross sections have been measured for alpha particles emitted in the bombardment of ${\mathrm{Au}}^{197}$ and ${\mathrm{Bi}}^{209}$ by ${\mathrm{C}}^{12}$, ${\mathrm{N}}^{14}$, and ${\mathrm{O}}^{16}$ projectiles at bombarding energies of 10.5 Mev/nucleon and for the C+Bi reaction at reduced energies of 8.7 and 7.1 Mev/nucleon. Angular distributions and absolute cross sections have also been measured for protons from the C+Bi and O+Bi reactions at bombarding energies of 10.5 Mev/nucleon. It was found that, from the angular distributions and energy spectra, it was possible to separate the contributions from direct and evaporation processes. The direct alpha particle results suggest that the principal direct process involved is the breakup of the incident projectile in an interaction with the surface of the target nucleus. At the 10.5 Mev/nucleon bombarding energies the cross sections for the emission of direct protons and direct alpha particles are found to be about 10% and 25-35%, respectively, of the calculated total reaction cross sections. The evaporation cross sections depend strongly on the excitation energy available in the compound system. The evaporation energy spectra can be fitted by an expression of the form $\mathrm{exp}(\ensuremath{-}\frac{{E}_{\ensuremath{\alpha}}}{T})$ and the results yield an average level density parameter, $a=22\ifmmode\pm\else\textpm\fi{}2$ ${\mathrm{Mev}}^{\ensuremath{-}1}$, for these reactions.