Neutron-proton bremsstrahlung from low-energy heavy-ion reactions.

Abstract

High-energy photon yields from the reactions $^{12}\mathrm{C}$${+}^{112,124}$Sn at 10 MeV/nucleon have been measured. The ratio of cross sections (${\mathit{E}}_{\ensuremath{\gamma}}$\ensuremath{\ge}30 MeV)\ensuremath{\sigma}${(}^{124}$Sn)/\ensuremath{\sigma}${(}^{112}$Sn) is 1.6\ifmmode\pm\else\textpm\fi{}0.2, which is larger than expected within the equal-participant model. The elementary n-p-\ensuremath{\gamma} cross section is evaluated within the neutral scalar \ensuremath{\sigma} meson exchange model, and implemented into a BUU code. The results of the BUU calculation suggest that the high-energy \ensuremath{\gamma}-ray yield differences for the two Sn isotopes arise from the differences in nucelon phase-space distributions. The sensitivity of the high-energy photon production to the initial phase-space conditions is explored.