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FACTORS DETERMINING THE ENERGY DEPENDENCE OF DELAYED NEUTRON YIELDS IN NEUTRON INDUCED FISSION
Authors & Affiliations
Pronyaev V.G., Piksaikin V.M.
Institute of Physics and Power Engineering, Obninsk, Russia
The scheme of parametrization of the energy dependence of delayed neutron yields (DNY) in neutron induced fission is proposed. It is based on "microscopic" approach, where the DNY for each precursor is obtained as a product of cumulative yield (CY) of this precursor on neutron emission probability Pn. The dependence of cumulative yields from incident neutron energy can be obtained from independent yields calculated with account ofthe following factors having a physical sense: I) contributions from different chances of fission; II) variation of mass independent yields with energy due to variations of contributions of different modes of fission (Symmetric, Standard I and Standard II); III) washing out of even-odd effects in charge distribution of fission fragment yields with increase of the neutron energy; IV) shift of distribution of fragment mass yields for a given isotope formed after emission of prompt neutrons because of variation of number of prompt neutrons with energy. The analysis was done for the energy region of the first fission chance of 235U and 237Np nuclei(neutron energy below 5.5 MeV). The different experimental data were used for a choice of parameters. It is shown, that DNY for fissioning nuclei with even and odd Z have rather different energy dependence and general decrease of DNY is explained mainly by variation of number of prompt neutrons with energy.
delayed neutron yields, cumulative output, the probability of neutron emission, fashion division, instant neutrons
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