The Spectrographic Determination of Uranium 235. Part III. Use of a Multiple Hollow Cathode Source Assembly and a 22 Foot Direct Reading Eagle Spectrograph

This report, the third of a series dealing with the isotopic analysis of uranium, describes the work done with a 22-ft Eagle mounted, direct-reading spectrograph using 5 in. of a 15,000 lines/in. concave grating in the second order. The samples were excited in a multiple source assembly consisting of 4 hollow cathode source lamps and an automatically positioned selector mirror. This arrangement allowed close comparison of unknown and standard, minimized the effect of exit slit misalignment, and allowed large number of routine samples to be handled economically. A complete analysis in duplicate, including comparison standards, was made in less than 20 min.

Measurements on 4 standards having U²³⁵ concentrations between 10 and 51% showed average external and internal precisions of ±0.23% and ±0.048% U²³⁵ for a single cathode determination. Analyses of 32 unknown samples containing 10-85% U²³⁵ determined independently on the optical spectrograph and the mass spectrometer, showed good agreement. Comparative measurements on 65 unknown samples in the range of 30-40% U²³⁵ showed an agreement of ±0.17% U²³⁵ with no significant bias. All precisions were expressed at the 95% confidence level. The factor limiting the precision—a weak line interfering with the U²³⁵ measurement, and the effect of U²³⁴ and U²³⁶ on the analysis are discussed.