Charged particle spectra: 140 MeVαparticle bombardment ofAl27,Ni58,Zr90,Bi209, andTh232

Abstract

Complete energy spectra and angular distributions of the light charged particles ($A\ensuremath{\le}4$) were measured for the bombardment of $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, $^{209}\mathrm{Bi}$, and $^{232}\mathrm{Th}$ with 140 MeV $\ensuremath{\alpha}$ particles. The spectral shapes of a given emitted particle are very similar for all target nuclei except in the region of the evaporation peak. The slopes of the energy spectra in the forward direction become steeper as the mass of the observed particle decreases and vary very rapidly with angles. The experimental data can be characterized by compound nuclear evaporation processes at low energies, or at backward angles, and by direct reactions, nonequilibrium components and projectile breakup processes at high energies and forward angles. The breakup cross section for $\ensuremath{\alpha}$ particles is found to be appreciable. The total yield of light charged particles is approximately a factor \ensuremath{\sim} 2 to 3 larger than the total reaction cross section for $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, and $^{90}\mathrm{Zr}$ and is \ensuremath{\sim} 0.7 of reaction cross section for $^{209}\mathrm{Bi}$ and $^{232}\mathrm{Th}$. The nonequilibrium light charged particle yield is of the order of 1000-1800 mb. The experimental results were analyzed using the pre-equilibrium exciton model, the compound nuclear evaporation model and a Serber type of model for the $\ensuremath{\alpha}$ particle breakup. The pre-equilibrium model calculations using a 5p-1h initial configuration reproduced the experimental angle-integrated energy spectra rather well.NUCLEAR REACTION $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, $^{209}\mathrm{Bi}$, $^{232}\mathrm{Th}$ ($\ensuremath{\alpha}$,$\mathrm{xp}$), ($\ensuremath{\alpha}$,$\mathrm{xd}$), ($\ensuremath{\alpha}$,$\mathrm{xt}$), ($\ensuremath{\alpha}$,$x^{3}\mathrm{He}$), ($\ensuremath{\alpha}$,$x\ensuremath{\alpha}$), ${E}_{\ensuremath{\alpha}}=140$ MeV; $\ensuremath{\theta}=20\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$, measured $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}d\ensuremath{\epsilon}}$, deduced $\frac{d\ensuremath{\sigma}}{d\ensuremath{\epsilon}}$ and $\ensuremath{\sigma}(E)$. Comparisons with preequilibrium exciton, evaporation and projectile breakup models.