Charge, mass, and energy changes during fragmentation of relativistic nuclei

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Abstract
We have examined the fragmentation of relativistic lanthanum and gold nuclei incident on targets of polyethylene, carbon, aluminum, and copper. Attention has been concentrated on those fragments whose atomic numbers were only changed by +1 to -3 from those of the incident nuclei. The cross section for the production of fragments with increased charge is about 10% that for fragments that have lost one charge, or about 1% of the total interaction cross section. We find that the velocity distributions of these fragments can be explained by assuming that they also lose significant numbers of neutrons when they pick up or lose charge, without a need to invoke any energy or momentum loss in the interaction, although we cannot exclude small losses. In particular, we cannot confirm the recent report of large energy losses during the charge pickup process. The relative numbers of neutrons lost can be represented by a simple Gaussian model, and, for those fragments with decreased charge, are much larger than the proton losses. These fragments consequently have large proton excesses and will be highly unstable.