EXCITATION-FUNCTIONS AND ISOMER-RATIOS IN THE REACTIONS NB-93(A,XN)(X=1-4)

Excitation functions and isomer ratios for 93Tc96Tc from the reactions 93Nb(α, xn) have been measured between 16 and 72 MeV. The excitation functions cannot be satisfactorily explained with a model assuming only a statistically-equilibrated compound nucleus, but the inclusion of pre-equilibrium processes produces a much better fit. The isomer ratio data (expressed as high spin/low spin) show a characteristic increase followed by a decrease in the tail of the excitation function. This is explained by taking explicit account of the distribution in spin arising from the initial interaction. When combined with hybrid (compound nucleus plus pre-equilibrium) model calculations, this provides a satisfactory explanation of the observed isomer ratios. The fall in isomer ratio arises from the increasing importance of pre-equilibrium processes in the tail of the excitation function, since these processes appear to produce residual nuclei with lower average spins than those formed by compound nucleus decay. © 1979.