Alpha-particle emission from the reaction 1354 MeV Ho-165 + Ta-181

of the reaction plane. Average velocity diagrams, a-particle energy spectra as a function of angle, and a-particle angular distributions are presented. The in-plane data show that the bulk of the a particles in coincidence with the deep-inelastic exit channel can be explained by evaporation from the fully accelerated fragments. The out-of-plane a-particle angular distribution data together with gamma-ray multiplicity data from previous work give a consistent picture of the transfer and partitioning of angular momentum between the two fragments. NUCLEAR REACTIONS ' 'Ta(' Ho, HI a)Elab — 1354 MeV: measured o (E,9,$ ), in- and out-of-plane anisotropies; deduced a-particle multiplicity, nuclear temperature. I. INTRODUCTION Compound nuclei deexcite predominantly by the evaporation of light particles (LP's). The energy spectra and angular distributions of these LP's contain information on the temperature (T) and spin (I) of the emitting nucleus. By studying the sequential LP decay from the fragments produced in deep-inelastic (DI) reactions, insight regarding the thermal properties and the angular momentum degrees of freedom associated with these reactions can be obtained. Two excellent examples of the use of LP's for these purposes are the studies of Eyal et al. ' and Babinet et al. In the former study, neutron emission from the reaction Er+ Kr at 7.0 MeV/nucleon was measured for the DI component of the reaction. This study concluded that the equilibration of the excitation energy between the two exit channel nuclei occurs during the lifetime of the intermediate complex. This conclusion is supported by two experimental observations. The first of these is that the mean number of evaporated particles from the two reaction products indicates that the partition of the total dissipated energy between the two fragments is in proportion to their masses. (Such a partition is required by the thermal equilibrium conditions. ) Detailed studies of neutron emission from the systems ' Ho + Fe at 8.5 MeV/nucleon and ' Au + Cu at 5.8 MeV/nucleon have reached the same conclusion. The second experimental observation is that the temperatures of the two fragments (deduced from the neutron energy spectra) are the same, within the experimental uncertainties. In the second example, in- and out-of-plane a-particle angular distributions were measured for the DI component of the reaction Ni+ Ar at 7.0 MeV/nucleon. The kinematics of this system allows the out-of-plane aparticle emission from the targetlike nucleus to be isolated by careful selection of the angle of the heavy ion detector as well as of the in-plane angle for the out-of-plane aparticle detectors. Individual fragment spins were extracted from the out-of-plane distributions as a function of mass asymmetry. The trend of these spins with mass asymmetry agreed with the rigid rotation predictions. This result was in agreement with earlier y-ray multiplicity (M&) work * on similar systems, which also suggests that rigid rotation was achieved during the lifetime of the DI complex. More recently, this conclusion has also been shown to be valid for the heavier system ""Ag+ Kr at 7.9 MeV/nucleon. The verification of rigid rotation for this near symmetric system is quite significant because M&