Evaluation of iodine and bromine isotope contribution in the process of delayed neutron emission

The daughters of the delayed-neutron precursors /sup 138/I and /sup 139/I (/sup 138/Xe and /sup 139/Xe) may decay under emission of both BETA particles and neutrons. If the branching coefficient is known, the contribution of a given isotope to the emitted delayed neutrons may be estimated. From published data it was estimated that the I isotopes (137, 138, and 139) do not yield more than 11% of the neutrons and not more than 4% of the delayed neutrons; the other I isotopes do not contribute hardly at all to the emission of delayed neutrons. For estimating the contribution of the Br isotopes, the known branching coefficient, 2%, of their decay process was used. Results of the calculation indicated that the number of neutrons attributable to the Br isotopes amounts to about 10% of the total delayed neutron yield, and in no case can it exceed 17%. Thus, the Br and I isotopes, which were considered the primary precursors of delayed neutrons, do not yield more than 20% of all the delayed neutrons. This may be explained by the fact that with the exception of /sup 87/ Br, none of the halide precursors possess a haif life coinciding with the halfmore » life of a given group of delayed neutrons; quite probably, each such group has a large number of precursors. (TTT)« less