Pre-equilibrium process for Lu175(p, xn ), Yb176(He3, xn yp), and Yb174,176(±, xn) reactions

The pre-equilibrium deexcitation process for (particle, xn yp) reactions induced by medium energy (40-120 MeV) light ions was studied by measuring singles -ray spectrum. The neutron multiplicity x following these reactions was identified by discrete rays characteristic of the (particle, xn yp) 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 Im of the yrast levels populated by the (particle, xn yp) reactions was found to be nearly constant in a wide range of the bombarding energy. The K-isomer population ratio for the Hf172 and Hf174 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. NUCLEAR REACTIONS Lu175(p, xn), x=2-5, E=40 MeV; Yb176(He3, xn yp) x=5-11, y=0-1, E=65-100 MeV; Yb174,176(±, xn), x=2-11, E=50-120 MeV; measured E, I; deduced median spin values, K-isomer population ratio. Enriched targets, HPGe, Ge(Li) detectors. Two phase deexcitation model analysis.