U235Thermal Neutron Fission Yields at Masses 90 and 91

Abstract

Thermal neutron fission yields in ${\mathrm{U}}^{235}$ have been determined for ${\mathrm{Sr}}^{90}$ and for ${\mathrm{Y}}^{91}$. The fission yield at ${\mathrm{Sr}}^{90}$ is 4.02 percent based on a half-life of 20 years. The yield for ${\mathrm{Y}}^{91}$, 5.35 percent, agrees within experimental error with that previously reported for ${\mathrm{Sr}}^{91}$. The apparent low yield at mass 90 is discussed.