Entrance and exit channel phenomena ind- andHe3-induced preequilibrium decay

Activation techniques were used to measure more than 30 excitation functions for single and multiple nucleon and/or $\alpha$ particle emission for $d$+${}_{}{}^{64,66}{}_{}{}^{}\mathrm{Zn}$, ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ with $E_d=9-26\mathrm{}$ MeV and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$+${}_{}{}^{63,65}{}_{}{}^{}\mathrm{Cu}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ with $E\left({}_{}{}^3{}_{}{}^{}\mathrm{He}\right)=10-44\mathrm{}$ MeV. The excitation functions are generally in agreement with the results of a combined equilibrium and preequilibrium hybrid model calculation applying initial exciton numbers $n_0=3\mathrm{}$ for $d$ and $n_0=4\mathrm{}$ for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ reactions. The composite system ${}_{}{}^{66}{}_{}{}^{}\mathrm{Ga}$ has been produced via $d$+${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$+${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ at excitation energies between 22 and 36 MeV. An entrance channel dependence shows up in the yields for single $p$- and $n$-emission when compared in the double ratio $R=\frac{\left[\frac{\sigma ({}_{}{}^3{}_{}{}^{}\mathrm{He}, p)}{\sigma ({}_{}{}^3{}_{}{}^{}\mathrm{He}, n)}\right]}{\left[\frac{\sigma (d, p)}{\sigma (d, n)}\right]}$. It approaches a value of about 2, indicating enhanced $p$ emission for the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-induced reaction. This value disagrees with the equilibrium isospin formalism and is best reproduced by initial particle exciton numbers