Pre-equilibrium process forLu175(p, xn γ),Yb176(He3, xn yp γ), andYb174,176(α, xn γ)reactions

The pre-equilibrium deexcitation process for (particle, $\mathrm{xn} \mathrm{yp} \gamma$) reactions induced by medium energy (40-120 MeV) light ions was studied by measuring singles $\gamma$-ray spectrum. The neutron multiplicity $x$ following these reactions was identified by discrete $\gamma$ rays characteristic of the (particle, $\mathrm{xn} \mathrm{yp} \gamma$) reaction residues. The neutron multiplicity distribution was found to depend on the projectile mass number. It suggests that the decaying neutrons depend on the initial exciton number at the pre-equilibrium phase. The median spin $I_m$ of the yrast levels populated by the (particle, $\mathrm{xn} \mathrm{yp}$) reactions was found to be nearly constant in a wide range of the bombarding energy. The $K$-isomer population ratio for the ${}_{}{}^{172}{}_{}{}^{}\mathrm{Hf}$ and ${}_{}{}^{174}{}_{}{}^{}\mathrm{Hf}$ depends on the projectile mass. The neutron multiplicity distribution was analyzed in terms of a simple two phase deexcitation model. The pre-equilibrium temperature, the number of particles emitted at the pre-equilibrium phase, and the exciton particle number at the preequilibrium phase (local mass) were deduced.