Isotopic analysis of uranium in tree bark by ICP mass spectrometry: A strategy for assessment of airborne contamination

Isotopic analysis of uranium in tree bark by ICP mass spectrometry is proposed as a new measurement strategy for monitoring airborne contamination and for discrimination of nuclear and nonnuclear emission sources. A quadrupole-based ICP mass spectrometer equipped with a microconcentric nebulizer and membrane desolvator was used to provide high-sensitivity measurement. The limit of detection for uranium (U-238) was 0.004 ng L-1. Measurement precision (U-235/U-238) was between 0.2 and 0.5% RSD for isotopic SRMs (U005 and U015; concentration, 1 mu g L-1) and ranged from 0.4 to 3.1% RSD for tree bark extracts (U concentration, 0.03-0.08 mu g L-1). Bark samples collected from the Peak District National Park in Derbyshire (U.K.) exhibited a natural 235U/238U isotope ratio value (0.0072) whereas samples from Sellafield, West Cumbria (U.K.) showed depletion in U-235 (U-235/U-238 = 0.0053-0.0064).