Nuclear Charge Distribution in Fission:Y92,Y93,Y94, andY95Independent Yields

Abstract

The fractional independent yields of ${\mathrm{Y}}^{92}$, ${\mathrm{Y}}^{93}$, ${\mathrm{Y}}^{94}$, and ${\mathrm{Y}}^{95}$ from thermal-neutron fission of ${\mathrm{U}}^{235}$ have been determined to be 0.0013\ifmmode\pm\else\textpm\fi{}0.0002, 0.016\ifmmode\pm\else\textpm\fi{}0.004, 0.08\ifmmode\pm\else\textpm\fi{}0.02, and 0.29\ifmmode\pm\else\textpm\fi{}0.08, respectively. The experimental method involved rapid separation of yttrium and strontium fission products by precipitation of yttrium hydroxide and subsequent radiochemical determination of the yttrium isotopes. Newly determined half-life values are 84\ifmmode\pm\else\textpm\fi{}5 sec for ${\mathrm{Sr}}^{94}$ and 33\ifmmode\pm\else\textpm\fi{}6 sec for ${\mathrm{Sr}}^{95}$. Gaussian curves which satisfactorily represent the nuclear charge dispersion for $A=92,93,94, \mathrm{and} 95$ have standard deviations $\ensuremath{\sigma}=0.58\ifmmode\pm\else\textpm\fi{}0.02,0.56\ifmmode\pm\else\textpm\fi{}0.02,0.56\ifmmode\pm\else\textpm\fi{}0.04, \mathrm{and} 0.53\ifmmode\pm\else\textpm\fi{}0.02$, respectively. The average value of $\ensuremath{\sigma}$ for ten mass numbers ($A=91\ensuremath{-}95 \mathrm{and} 139\ensuremath{-}143$) is 0.59\ifmmode\pm\else\textpm\fi{}0.02. For the individual mass numbers, a single Gaussian curve with $\ensuremath{\sigma}=0.59\ifmmode\pm\else\textpm\fi{}0.06$ (full width at half-maximum = 1.56\ifmmode\pm\else\textpm\fi{}0.12 charge units) gives a satisfactory representation of nuclear charge dispersion.