Deformation effects in 56 Ni nuclei produced in 28 Si + 28 Si at 112 MeV

Velocity and energy spectra of the light charged particles emitted in the ${}^{28}\mathrm{Si}{(E}_{\mathrm{lab}}=112 \mathrm{MeV}{)+}^{28}\mathrm{Si}$ reaction have been measured at the Strasbourg VIVITRON Tandem facility. The ICARE charged particle multidetector array was used to obtain exclusive spectra of the protons and $\ensuremath{\alpha}$ particles in the angular range $15\ifmmode^\circ\else\textdegree\fi{}\char21{}150\ifmmode^\circ\else\textdegree\fi{}$ and to determine the angular correlations of these particles with respect to the emission angles of the evaporation residues. The experimental data are analyzed in the framework of the statistical model. The exclusive energy spectra of $\ensuremath{\alpha}$ particles emitted from the ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ compound system are generally well reproduced by Monte Carlo calculations using spin-dependent level densities. This spin dependence approach suggests the onset of large nuclear deformation at high spin. A reanalysis of previous $\ensuremath{\alpha}$-particle data from the ${}^{30}\mathrm{Si}{+}^{30}\mathrm{Si}$ compound system, using the same spin-dependent parametrization, is also presented in the framework of a general discussion of deformation effects in the ${A}_{\mathrm{CN}}\ensuremath{\approx}60$ mass region.