Strong impact parameter dependence of hard photon production in intermediate energy heavy ion collisions

The dependence of the high energy photon production on the impact parameter has been investigated in the reaction ¹²⁹Xe+ ¹⁹⁷Au at 44 MeV/u using the multidetector array MEDEA. A strong dependence of the high energy photon production probability on the impact parameter has been observed, while the slope parameter of the photon spectrum is almost constant. The data support the interpretation of the hard photon production in terms of first chance n-p collisions.