The yield of 49, the efficiency of production of 49, and poisoning in a power plant are discussed. Only the crudest of estimates of the poisoning are possible: these indicated that production will probably not be hampered by poisoning. In this case the yield of 49 could be as high as 3 kg/ton but only about 2 kg/ton is compatible with a fairly high efficiency. In the case that production is stopped by poisoning, smaller yields, proportional to the tolerable loss in k, are obtained. In this case the yield will be improved by a factor of 2 or 3 if only the most poisoned parts are extracted and replaced by new uranium.

Abstract. The effect of the neutron flux on the relative importance of different fission product poisons is discussed. The general expression for the poising of a fission product is given with the various equations for special cases of interest. The formulae are applied to the problem of finding the poisoning due to fission products at the end of one day in a pile operating with a flux of 4 x 10(14) neutrons/cm(2)/soc. These results are summarized in the table on page 12. Appendix I contains a revised list of cross sections x yields for all stable isotopes. Such a list was first given by Wheeler in CP-889. Appendix II contains a list of radioactive fission products with half lives greater than one day with data about yields, parents, gaseous ancestors, and numbers of neutrons.