Energy spectra and angular distributions have been measured for 46 isotopically separated Li through Mg fragments produced in reactions of 480 MeV protons with Ag. This silicon solid state detectors have been used with time-of-flight techniques to extend measured fragment energies as low as 1 MeV per nucleon, well below the most probable fragment energies. Reasonable fits to the relatively small evaporative components of the spectra are obtained using a self-consistent calculation previously developed. An analysis of the remaining nonevaporative components using contours of relativistically invariant cross section in the plane of rapidity and perpendicular momentum indicates that these components can be described in terms of isotropic emission from moving sources if the source velocity is allowed to be a function of the fragment's radial velocity in the source frame. The relationship between these velocities is essentially independent of fragment $Z$ and $A$. Coupled with the evaporation calculation, this relationship allows all spectra to be reasonably fit at all angles by use of a simple (four parameters per fragment) phenomenological form for the isotropic nonevaporative component in the moving source frame. While such a form might suggest a statistical origin for the nonevaporative components, detailed consideration of the parameters required suggests difficulties with such an interpretation. Implications of these data for other models are discussed. Energy integrated and total cross sections are calculated.

• Received 21 November 1983

DOI:https://doi.org/10.1103/PhysRevC.29.1806