Keith Fifield

Global cooling initiated stony deserts in central Australia 2–4 Ma, dated by cosmogenic 21Ne-10Be

Stony deserts are durable indicators of aridity but until now have not been directly dated. Using 21Ne and 10Be produced in surface rocks by cosmic rays, we show that Australian stony deserts formed 2–4 Ma, at the time when global cooling initiated the Quaternary ice ages and intensified aridity-induced major landscape changes in central Australia. This is the first direct determination of stony desert ages, using a new method for determining cosmogenic 21Ne in the presence of various neon components from other sources.

Plutonium measurement using accelerator mass spectrometry: Methodology and applications

The generally low levels of plutonium in environmental samples, often combined with limited sample sizes, necessitate reliable low-level techniques for determination of Pu isotopes. Accelerator mass spectrometry (AMS) has proved to be a powerful method for measuring low-level Pu activity concentrations and Pu isotope ratios. Based on procedural blanks, detection limits for AMS were below 1 fg Pu (equivalent to ca. 2 uBq 239Pu), which can compete with both TIMS, high sensitivity ICP-MS, and certainly alpha-spectrometry, while showing less interference, memory and matrix effects as compared to routine ICP-MS techniques. In addition to low detection limits, the technique offers the advantage of giving information on Pu isotope ratios. Determination of Pu isotopes in samples collected from the Mayak area indicated that the ratio of 240Pu/239Pu in waste has increased towards the present and suggested that most of the plutonium in the Upper Techa River originates from the early waste discharges, although enhanced atom ratios in surface sediments downstream indicate a contribution from other sources. Measurement of sediments collected from dumping sites at Novaya Zemlya showed deviations from global fallout 240Pu/239Pu ratios.