Spallation of $^{32}S$ ions at ultra-relativistic energies in nuclear emulsion

Partial production cross sections of electromagnetic breakup of $^{32}S$ projectiles at two widely differing energies were measured using an emulsion target. The electromagnetic dissociation represents about 6% and 17% of the total number of nuclear events at E//l//a//b /A = 3.7 and 200 GeV, respectively. The experimental electromagnetic cross sections sigma//E//M//D**e**x**p show an energy dependence that is well reproduced by the Weizsacker-Williams approximation. The value of sigma//E//M//D**e**x**p at 200A GeV (with gamma very much greater than 1) shows a good agreement with that predicted by the combined model of Pshenichnov et al. Examination of the reactions (gamma, p) and (gamma, He) reveals that the ratio of 1 p/1 He cross sections is close to unity at Dubna energy (3.7A GeV), while it rapidly increases to 3.0 plus or minus 0.6 at CERN energy (200A GeV). In most of the observed dissociation modes, the total kinetic energy of the fragments in the projectile rest frame is lower than 50 MeV. Nevertheless, it is possible that the contribution of excitation modes of the different multipolarities is determining in this region. 30 Refs.