234U/238U activity ratios

We are currently utilizing ²³⁴U/²³⁸U measurements in isotope hydrology studies. For larger samples, measurement of the ²³⁴U/²³⁸U ratio is accomplished by a two sequence dynamic analysis, peak-switching the ²³⁵U beam between Faraday cup and Daly detector to establish a real time gain, and fractionation correcting relative to the known ²³⁵U/²³⁸U ratio. Alternatively, for small samples, the same measurement is made by peak jumping all isotopes (including ²³⁸U) into the Daly detector due to its large dynamic range. Using the latter method and maintaining a 1 Mcps ²³⁸U beam, the external reproducibility of the ²³⁴U/²³⁸U ratio in an in-house secular equilibrium U standard is 0.00005493 ± 10 (0.18%; 1-sigma, n=37; accepted value=0.00005489).