Cross sections for 74, 76, 77,788e(n ' p) 74, 76, 77, 78As ' 76Se(n ' 2n)TSSe and 8~ ~)77Ge reactions have been measured in the energy range from 13.0 to 16.6 MeV by the activation technique using Ge(Li) detector 7-ray spectroscopy. Samples of selenium of natural isotopic composition were used as targets. The measurements provide information on the evolution of the (n, p) excitation functions with the increasing target neutron number (isotopic effect). The reaction model combining the compound nucleus and the preequilibrium emission processes is used to interpret these three types of reactions. The isotopic trend for the (n, p) reactions due to the neutron-proton competition in the compound nucleus is satisfactorily reproduced. However, a further experimental and theoretical work is needed for a better understanding of the origins of discrepancies which are suggested to be related to the precompound aspects of the assumed reaction model.

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Crosssections for 7~ (n, p) 7~ 7~ 2n)69Ge, 72Ge (n, c~)69Zn m and 74Ge(n, c~)71Znm reactions are measured in the energy range from 13.0 to 16.6 MeV by the activation method using Ge (Li) detector 7-ray spectroscopy and compared with predictions of the reaction model incorporating preequilibrium and equilibrium emission mechanisms to interpret the energy dependence of the isotopic effect occuring in the (n, p) reaction. The fitted single-particle state-density parameters g, determined here for the germaniums are discussed together with the g-values found previously for the Se, Zr and Pd isotopic chains. A validity of the consistency condition between the precompound and compound models, which relates g to the experimental level-density parameter a via a = gZg/6 is demonstrated. PACS: 25.40.Fq

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