A direct probe of the in-medium pn scattering cross section

Hard photon production from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions is examined as a probe of the in-medium pn scattering cross section within a transport model. Uncertainty of photon production probability pn -> pn gamma is cancelled out by using the ratio of hard photon spectra R-12C+ 12(C/p+n) (gamma) from two reactions. The in medium pn scattering cross section is constrained by using the ratio of hard photon production cross sections of proton-induced reactions p + C-12 and p + H-2. A reduction factor sigma(medium)(pn)/sigma(free)(pn) of about 0.5-0.7 around saturation density is obtained by comparing with the existing experimental data. (C) 2011 Elsevier B.V. All rights reserved.