Emission times in low-energy heavy-ion reactions by particle-particle correlations

Particle-particle correlations (p-p and \ensuremath{\alpha}-\ensuremath{\alpha}) vs relative momentum (${P}_{\mathrm{rel}}$) are reported (${\ensuremath{\theta}}_{\mathrm{lab}\mathrm{\ensuremath{\approxeq}}19.5}$\ifmmode^\circ\else\textdegree\fi{}) for the reaction 140 MeV $^{16}$O${+}^{27}$Al. A plot of the Galilean invariant cross section indicates that evaporative emission dominates the gross proton production even at this forward angle. The observed anticorrelation between two protons for small values of ${P}_{\mathrm{rel}}$ is analyzed to give an evaporation lifetime in the range of 1--5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ s. The \ensuremath{\alpha}-\ensuremath{\alpha} correlation is completely different; it seems to arise from preformed $^{8}\mathrm{Be}$.