Two-neutron relative-momentum correlation functions have been measured in the 130 MeV ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ reaction. Differences in the longitudinal and transverse correlation functions, observed for the first time for neutrons, allow an independent determination of the spatial extent and the time scale for decay of the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ compound nucleus. A comparison with theoretical calculations indicates a radius of 4.4±0.3 fm and an average neutron emission time scale of 1100 ± 100 fm/c for ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ at 100 MeV excitation energy. Correlation functions selected by cuts on the total momentum of the neutron pair give a quantitative characterization of the cooling of a compound nucleus.

• Received 10 April 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.4190