Large-angle correlations in evaporative particle emission: shape distortion, surface expansion

Evaporation-like emission of light particles (n, H, He...) has been observed for many nuclear reactions that populate composite nuclei with temperatures of up to ≅ 5 MeV and spins as high as ≅ 150 h. The measured average energies for the light charged particles are often significantly lower than calculations for evaporation from spherical nuclei. Detailed calculations have not been reported for the role of deformation in evaporative emission patterns, and thus the interpretation of such data has been severely limited. In this paper we describe a method for making evaporation calculations for deformed nuclei, and we present results for several systems. The trends of the calculated results are compared to those for spherical emitters in order to get a feeling for those effects peculiar to the deformations. The patterns of calculated spectra and angular distributions encourage the notion that such studies can give valuable clues to the shapes and surface properties of these very hot nuclei. Comparisons are made to experimental data for 1H-4He and 4He-4He correlations in the reaction 337 MeV 40Ar + natAg. These comparisons point out some novel features of the nuclear surface