[1] Open Univ, Dept Earth Sci, Milton Keynes MK7 6AA, Bucks, England
[2] Oxford Instruments Analyt Ltd, High Wycombe HP12 3SE, Bucks, England
[3] Univ Vienna, Atominst, A-1020 Vienna, Austria
[4] Glasgow Caledonian Univ, Glasgow G4 0BA, Lanark, Scotland
[5] W Xray Solut Ltd, Sheffield S11 9NF, S Yorkshire, England