Space-time evolution of the reactionsN14+27Al,Au197atE/A=75 MeV andXe129+27Al,Sn122atE/A=31 MeV probed by two-proton intensity interferometry

Two-proton correlation functions have been measured at ${\mathrm{\theta }}_{\mathrm{lab}}$≊25° for the ‘‘forward kinematics’’ reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ${+}^{27}$Al, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ${+}^{197}$Au at E/A=75 MeV, for the ‘‘inverse kinematics’’ reaction ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ ${+}^{27}$Al at E/A=31 MeV, and for the nearly symmetric reaction ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ ${+}^{122}$Sn at E/A=31 MeV. For the reactions at 75 MeV per nucleon, the correlation functions exhibit pronounced maxima at relative proton momenta, q≊20 MeV/c, and minima at q≊0 MeV/c. These correlations indicate emission from fast, nonequilibrium processes. They are analyzed in terms of standard Gaussian source parametrizations and compared to microscopic simulations performed with the Boltzmann-Uehling-Uhlenbeck equation. For the reactions at 31 MeV per nucleon, the two-proton correlation functions do not exhibit maxima at q≊20 MeV/c, but only minima at q≊0 MeV/c. These correlations indicate emission on a slower time scale. They can be reproduced by calculations based on the Weisskopf formula for evaporative emission from fully equilibrated compound nuclei. For all reactions, the measured longitudinal and transverse correlation functions are very similar, in agreement with theoretical predictions.