Energy Dependence of the Isotopic Effect in the (n,p) Reaction on Medium Weight Nuclei

Abstract

Excitation functions for the (n,p) reaction on the ^70,72,73,74Ge, ^74,76,77,78Se, ^90,91,92,94Zr and ^106,108Pd nuclei were measured in the neutron energy range from 13 to 16.6 MeV with the aid of the activation method. Neutrons were produced with the T(d,n)⁴He reaction in the Ti-T target. The cross sections decrease exponentially with increasing target asymmetry parameter (N_t-Z_t)/A_t (isotopic effect) at fixed neutron energies for each of the studied Isotopes. The slope coefficients of the exponent are found decreasing functions of energy for the Ge and Se series while for Zr they stay approximately constant in the investigated energy range. The data are interpreted in terms of the reaction model incorporating preequilibrium and equilibrium emission processes. The differences in energy dependence of the Isotopic effect are ascribed by the assumed reaction model to the compound component which slopes more steeply with (N_t-Z_t)/A_t than the precompound one and whose relative contribution decreases with increasing Z_t.