T. Reposeur

Impact parameter dependence of high energy gamma ray production in heavy-ion collisions☆

Abstract High energy photons ( E γ ⩾30 MeV) have been measured in coincidence with light particles observed in a multidetector array for the 40 Ar+ 51 V system at a bombarding energy of E A =65 MeV . Double differential cross sections were obtained as a function of the midrapidity charge representation of the centrality of the collision. The inverse slope parameter increases with centrality more strongly than predicted by a BUU model.

Mass dependence of pion production in heavy ion collisions near, but below threshold☆

Abstract We have measured the inclusive cross section for production of negative pions near mid-rapidity in 20 Ne + NaF , 139 La + 139 La and 197 Au + 197 Au collisions at E = 183 and 236 MeV/u. Au + Au is the heaviest system from which subthreshold pion production has been measured to date. The dependence of the pion cross section on pion energy, beam energy and associated charged particle multiplicity is consistent with previous results both above and below threshold. The dependence of the cross section on the mass of the colliding system varies only slightly as the beam energy is reduced below threshold, in contrast to some previous measurements. Comparison with theory suggests that at these energies the pion production process is still dominated by nucleon-nucleon collisions.

Target isotope effect in high energy photon production atE/A=10 MeV

A comparison has been made between the production of high energy (Eγ≧30 MeV)γ rays from the bombardment of124Sn and112Sn targets withE/A= 10 MeV12C ions. The results are well explained by then-p bremsstrahlung model and do not indicate the need for any new processes.