The Quasi-Elastic Region of the IRON-56+IRON-56 and IRON-56+URANIUM-238 Reactions
Projectile-like fragments (PLF's) were detected for the 15-MeV/uFe+Fe and Fe+U reactions. The mass, charge and energy of the PLF's were recorded. For the Fe+Fe reaction light-charged particles were also recorded in coincidence with PLF's. Products with kinetic energies corresponding to the first 100 MeV of energy loss were studied in detail for a variety of questions that remain concerning the quasi -elastic region. PLF energy spectra clearly show the presence of structures. These structures can be classified as either narrow or broad in kinetic energy width. By use of evaporation calculations, it was shown that broad structures were due to normal evaporation processes. Narrow structures with widths of 8 to 10 MeV could not be duplicated by evaporation calculations and their origin is still unexplained. The evaporation peaks seen in the cobalt isotope energy spectra were used to determine the mean value of the excitation energy division (EED) since it was shown that this is the main determining factor in the value of the evaporation peak centroid. The results of the EED determinations indicate that many model assumptions of excitation energy division with nucleon exchange may be inapplicable during the first stages of interaction. The variance of the EED was determined for certain cobalt isotopes by use of an iteractive fitting program based on the evaporation process. For the 15-MeV/u systems it was found that the EED variance was smaller than what would be predicted by Morrissey's thermal variance. The optimum Q-values for cobalt isotopes were found to be effected by evaporation processes. After evaporation corrections to these values, it was found that Siemen's optimum Q-value model accurately predicted all values for the Fe+U system and most values for the Fe+Fe system. The exception was for the one proton transfer to ('57)Co in the Fe+Fe system, which has a much larger optimum Q-value than predicted. This may indicate a fundamental difference in proton transfer between Fe and U targets.
- Pub Date:
- Physics: Nuclear