Investigation of an alleged nuclear incident at Greenham Common Airbase using Tl-mass spectrometric measurements of uranium isotopes

Uranium isotopic compositions were determined in over 500 soil samples from the Greenham Common Air Base and in surrounding west Berkshire and north H ampshire, England to detect potential contamination from an alleged 1958 nu clear incident. Owing to the large number of samples collected for the stud y, the short reporting time expected, and the potentially subtle nature of any contamination, a rapid and highly precise method of uranium analysis wa s developed. High precision U-238/U-235 mass spectrometric measurements are required to see slight excesses in any anthropogenic component. The reprod ucibility for measurements of uranium isotopic ratios in standards and soil samples was better than 0.26% at the 3 sigma uncertainty level. Despite an intensive study around the airbase no evidence was found for any contamina tion by uranium of anomalous isotopic composition. Plutonium measurements w ere also made to support the U analysis and were found to be consistent wit h atmospheric bomb fallout for the United Kingdom. The detection of subtle (though radiologically insignificant) amounts of U contamination around a n earby nuclear weapons site illustrates the usefulness and effectiveness of this approach in environmental surveys.