Angular distributions and energy spectra of fragments formed in the interaction of $\sp{238}$U with 400 GeV protons

David Lewis Klingensmith, Purdue University


Angular distributions and differential ranges at five angles to the beam have been measured for 23 fragments, ranging from $\sp{47}$Ca to $\sp{143}$Ce, produced in the interaction of $\sp{238}$U with 400 GeV protons. The angular distributions have been characterized by the two model-independent parameters, A$\sb1$ and A$\sb2$, which determine the asymmetry and anisotropy, respectively. The normalized angular distributions (differential cross sections) have been used to normalize the energy spectra obtained from the data to yield values for the double differential cross section. The energy spectra show evidence for the presence of two components, which can be attributed to deep spallation and to fragmentation or fission. The spectra have been compared with a thermal model, used to test the two-step model of high-energy reactions, subjected to an invariant cross section analysis, and compared with the predictions of the Hufner fast breakup model.^ The energetic component was fit with a thermal fragment emission model and was found to be consistent with binary fission and, for the lightest products, with fragmentation. The model fits provided a means of quantitatively separating the components. The low-energy component was found to be consistent with a deep spallation mechanism. Physical parameters calculated for both components were within the expected ranges.^ The formation of most products was determined to be inconsistent with the two-step model. An invariant cross section analysis of the high-energy component suggests that peaks at sideward angles reflect the intrinsic angular distributions. No significant correlation between source and fragment velocities was found. The deep spallation component was found to be emitted from a source moving at large angles to the beam. Physical parameters calculated from the data with the fast breakup model were within expected ranges, with the exceptions of the width of the spray particle momentum distribution and the Coulomb angle. ^




Major Professor: Norbert T. Porile, Purdue University.

Subject Area

Chemistry, Nuclear

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