Nuclear Charge Distribution in Fission: ${\mathrm{Y}}^{92}$, ${\mathrm{Y}}^{93}$, ${\mathrm{Y}}^{94}$, and ${\mathrm{Y}}^{95}$ Independent Yields

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±0.0002, 0.016±0.004, 0.08±0.02, and 0.29±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±5 sec for ${\mathrm{Sr}}^{94}$ and 33±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 $\sigma =0.58\mathrm{}\pm 0.02,0.56\pm 0.02,0.56\pm 0.04, \mathrm{and} 0.53\pm 0.02$, respectively. The average value of $\sigma$ for ten mass numbers ($A=91\mathrm{}-95 \mathrm{and} 139-143$) is 0.59±0.02. For the individual mass numbers, a single Gaussian curve with $\sigma =0.59\mathrm{}\pm 0.06$ (full width at half-maximum = 1.56±0.12 charge units) gives a satisfactory representation of nuclear charge dispersion.