Pre-equilibrium helion emission induced by protons

[摘要] This thesis is devoted to a study of the 93Nb( p r ,3He) and 59Co( p r ,3He) reactions at incidentenergies of 100 MeV, 130 MeV and 160 MeV. Double differential cross sections andanalysing power distributions were measured from a threshold of ~30 MeV up to thekinematic maximum and at scattering angles between 15º and 120º. The experimental datawere compared with theoretical calculations done by combining a statistical multistep theorywith a deuteron pickup mechanism in the final stage. The contribution of the first three stepstowards the total double differential cross section and analysing power was assessed.The theory described the experimental double differential cross section and analysing powerdata reasonably well over all incident and scattered energies and for both target nuclei. Asthe incident energy was increased, the characteristics of the reaction mechanism alsoremained consistent. Thus the results supported the underlying multistep-pickup theory. Thetwo target nuclei demonstrated similar responses, suggesting these two share the same basicreaction mechanism.The total double differential cross section for the reaction dropped with an increase inincident energy. At a fixed emission energy, near the maximum allowed value, the slope ofthe double differential cross section increased with an increase in incident energy, resulting inthe dominance of forward peaked reactions at higher incident energies.The sensitivity of analysing power to the multistep part of the reaction was valuable to thestudy. Forward-peaked contributions that were associated with single step direct reactionsresulted in large analysing power values at small scattering angles, and values dropped toaround zero at large angles. The analysing power also appeared to decrease to valuesapproximating zero as the incident energy was increased to 160 MeV. Furthermore, thisstudy also confirmed the dominance of higher step mechanisms at high excitation energies,irrespective of incident energy. In general the results were in agreement with the predictedproperties of the assumed reaction mechanism at all incident and emission energies, whichinspires confidence that the theoretical interpretation is likely to be correct.

[发布机构] Stellenbosch University