Relative yield of delayed neutrons and half-life of their precursor nuclei with fissioning of 239Pu by 14.2-17.9 MeV neutrons

The energy dependence of the relative yield of delayed neutrons and of half-lives of their precursor nuclei with fissioning Pu-239 by 14.2-17.9 MeV neutrons is measured. The data obtained are analyzed in terms of the average half-life < T > of the precursor nuclei of the delayed neutrons. It is shown that the observed growth of < T > with increasing primary neutron energy in the energy range studied is due predominately to opening of the channels for the emission fission of nuclei. Comparing the data on the average half-life of the precursor nuclei of delayed neutrons obtained in the present work with those obtained by other authors showed that the anomalously high values of < T > are due to methodological features of the experiment which are related with the properties of the reaction T(d, n)He-4 used as a neutron source on electrostatic charged-particle accelerators. The data obtained are of great value for developing instrumentational nondestructive means for determining the nuclide composition of nuclear fuel based on the detection of delayed neutrons.