1. Earth and Environmental Systems Institute and Department of Geosciences; Pennsylvania State University; University Park Pennsylvania USA
2. Now at College of Earth, Ocean and Atmospheric Sciences; Oregon State University; Corvallis Oregon USA
3. Geology Department; University of Vermont; Burlington Vermont USA
4. Department of Geological Sciences; University of Texas; El Paso Texas USA
5. AMS Laboratory; Scottish Universities Environmental Research Centre; East Kilbride UK
6. Earth Research Institute; University of California; Livermore California USA