The decay constant of 234U revisited

The decay constant of 234U revisited


J.P. Bernal, M.T. McCulloch, G.E.Mortimer and T.Esat

A new approach has been used to measure the abundance of 234U in samples in secular equilibrium with improved precision and accuracy. Taking advantage of the several features of the new NEPTUNE MC-ICP-MS, we have been able to measure concentrated solutions of previously well characterized uranium standards (HU-1 and

ALH). As a result, an 234U ion beam was created with sufficient intensity to be measured on a Faraday cup. Using a calibrated 233U-236U calibrated double-spike, themulticollection, combined with high and low mass-resolution modes a 234U/238U isotope ratio for samples in secular equilibrium of (54.67 ( 0.026 ( 10-6) has been obtained (Figure 7), in excellent agreement with measurements from other laboratories, but with a three-fold improvement in precision. Hence, a revised, and more precise, decay constant (2.837(10-6 ( 1.3(10-9) and half-life (244,290 ( 120 y) of 234U has been obtained (Figure 8).

Figure 7: Repeat measurements of 234U/238U in secular equilibrium standards using high and
low- resolution. Low-resolution data has better precision due to higher ion-beam intensity.

Figure 8: The half-life of 234U calculated in this work compared to previously accepted values.