Preequilibrium decay of nuclei withA≃90at excitation energies to 100 MeV

Abstract

Calculations have been made of the excitation functions of 28 nuclear reactions induced by 10-100 MeV protons incident upon targets in the mass region, $A=90$. Eleven of these reactions have mechanistic components arising from the emission of $\ensuremath{\alpha}$ particles. Similar calculations have been made of the proton and $\ensuremath{\alpha}$ particle spectra for 62 MeV protons incident on $^{89}\mathrm{Y}$. The results of all of the calculations have been compared with the appropriate experimental data. The calculations utilize the theoretical framework of the preequilibrium exciton model for nuclear reactions in conjuction with conventional evaporation theory. A number of recent advances in the computation of equilibration and emission rates, state densities, and the nucleon mean free path have all been incorporated. In addition, introduction of a preformation factor allows the inclusion of $\ensuremath{\alpha}$ particle emission in both the preequilibrium and evaporation stages of the calculation. Agreement between the calculations making use of no freely varying parameters and all of the experimental data is excellent. In particular, the theoretical model has reproduced the excitation functions for both simple ($p,n$) and complex ($p,4p6n$) reactions, at proton energies varying over nearly 100 MeV, for peak cross sections of as little as 1 mb to as great as 1000 mb, including the reproduced showing the characteristic double humped curve indicative of $\ensuremath{\alpha}$ particle emission. Equally well reproduced are the differential proton and $\ensuremath{\alpha}$ particle energy spectra. The characteristics of the reaction model are discussed with particular reference to the consequences of the more recent advances in the theory mentioned above.NUCLEAR REACTIONS $^{88}\mathrm{Sr}(p,xn)$, $x=3\ensuremath{-}5$, ($p,p3n$), ($p,2p\mathrm{xn}$), $x=1,3,4$; $^{89}\mathrm{Y}(p,xn)$, $x=1,3,4$, ($p,pxn$), $x=3\ensuremath{-}5$; $^{90}\mathrm{Zr}(p,xn)$, $x=1,2$, ($p,2p\mathrm{xn}$), $x=1\ensuremath{-}5$, ($p,3p\mathrm{xn}$), $x=3,5,6$, ($p,4p\mathrm{xn}$), $x=3\ensuremath{-}6$; $^{89}\mathrm{Y}$, $p$ and $\ensuremath{\alpha}$ spectra; $E=10\ensuremath{-}100$ MeV; calculated $\ensuremath{\sigma}(E)$, ${E}_{p}$, ${E}_{\ensuremath{\alpha}}$. $^{88}\mathrm{Sr}$, $^{90}\mathrm{Zr}$; enriched target.