Independent isomer yield ratio ofRb90from thermal neutron fission ofU235

The independent isomer yield ratio for ${}_{}{}^{90}{}_{}{}^{}\mathrm{Rb}$ from thermal neutron fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ has been measured by use of a new technique involving a pulsed reactor and an on-line mass spectrometer facility. The apparent isomer yield ratio was measured for several ion collection time intervals of different durations and extrapolated to zero collection time to eliminate interference from ${}_{}{}^{90}{}_{}{}^{}\mathrm{Kr}$ decay. The observed independent isomer yield ratio of 8.7±1.0 for ${(}^{90}$ ${\mathrm{Rb}}^{\mathrm{m}}$ ${)/\mathrm{}}^{90}$ ${\mathrm{Rb}}^{\mathrm{g}}$) is one of the largest ratios measured for a low energy fission process. However, a statistical model analysis shows that the average angular momentum (〈J〉=4.5) deduced from this isomer yield ratio is consistent with average angular momentum for several other products from low energy fission.