AbstractThe thermal fission yields of 43 mass chains for233U,235U,239Pu, and241Pu and the fast reactor fission yields of 45 mass chains for235U and239Pu have been measured with a relative standard deviation of 1 to 2%. The data were obtained mainly by measuring long-lived and stable fission products by the technique of isotope dilution mass spectrometry. This paper has two sections: the first reports the fission yields, the second describes the chemical analysis techniques for the fission products.