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

High-energy photon yields from the reactions ¹²C{+}112,124$Sn at 10 MeV/nucleon have been measured. The ratio of cross sections (${E}_{{γ}}≥30 MeV)σ{(}¹²⁴Sn)/σ{(}¹¹²$Sn) is 1.6±{}0.2, which is larger than expected within the equal-participant model. The elementary n-p-{γ} cross section is evaluated within the neutral scalar {σ} meson exchange model, and implemented into a BUU code. The results of the BUU calculation suggest that the high-energy {γ}-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.