Spontaneous Fission Yields ofCf252

Abstract

A radiochemical investigation has been made of the fission yield curve for the spontaneous fission of ${\mathrm{Cf}}^{252}$. One source of 1\ifmmode\times\else\texttimes\fi{}${10}^{6}$, another of 2\ifmmode\times\else\texttimes\fi{}${10}^{7}$, and a third of 7\ifmmode\times\else\texttimes\fi{}${10}^{7}$ fissions per minute were used to obtain the data. Thirty-six radioactive nuclides between mass numbers 77 and 166 were separated, identified, and their fission yields calculated. Upper limits were set for nine other nuclides. The fission yield curve has maxima of 6.05% at masses 107 and 141, with a "full width at $\frac{1}{10}$ maximum" of each peak of approximately 27 mass units. There is a very narrow "trough" with a minimum value of \ensuremath{\leqq} 8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$% at mass number 124. In addition, while the curve as a whole is symmetrical about mass 124, each peak is not symmetrical about its own maximum, being significantly spread toward the most asymmetric fission modes. A small finestructure peak was observed at mass 113. No evidence was seen of activities that could be ascribed to ternary fission events, upper limits of ${10}^{\ensuremath{-}4}$% fission yield being set for individual nuclides between mass numbers 28 and 72.