Large discrepancies have been observed between measured Electromagnetic Dissociation(ED) cross sections and the predictions of the semiclassical Weizäcker-Williams-Fermi(WWF) method. In this paper, the validity of the semiclassical approximation is examined. The total cross section for electromagnetic excitation of a nuclear target by a spinless projectile is calculated in first Born approximation, neglecting recoil. The final result is expressed in terms of correlation functions and convoluted densities in configuration space. The result agrees with the WWF approximation to leading order(unretarded electric dipole approximation), but the method allows an analytic evaluation of the cutoff, which is determined by the details of the electric dipole transition charge density. Using the Goldhaber-Teller model of that density, and uniform charge densities for both projectile and target, the cutoff is determined for the total cross section in the nonrelativistic limit, and found to be smaller than values currently used for ED calculations.In addition, cross sections are calculated using a phenomenological momentum space cutoff designed to model final state interactions. For moderate projectile energies, the calculated ED cross section is found to be smaller than the semiclassical result, in qualitative agreement with experiment.
In this report, electric quadrupole corrections to the two neutron removal cross section measured in heavy ion collisions are estimated for 197 Au and 59 Co targets. The quadrupole process is assumed to proceed primarily through excitation of the giant isovector quadrupole resonance, which then decays by neutron emission. For 59 Co, the contribution from E2 radiation is found to be small, while for 197 Au we find the quadrupole contribution resolves the discrepancy between experiment and the simple predictions of the Weissacker-Williams virtual photon method.
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