C-14 AMS AT THE UNIVERSITY OF WASHINGTON - MEASUREMENTS IN A SHARED FACILITY AT THE 1-PERCENT LEVEL ON 0.4 MG SAMPLES

The FN tandem accelerator at the University of Washington has been used for AMS measurements for more than ten years. The current sample preparation methods, measurement procedures and system capacity are described. Preliminary results of an ongoing study of (CH4)-C-14 in atmospheric methane and methane from wetlands environments are presented. The development of new preparation methods has reduced our sputter-source sample size requirements from 2-4 mg to 200-400-mu-g and allows essentially complete utilization of the sample during the sputtering process. At the +/- 1% level, the current precision and accuracy of our measurements are limited by counting statistics uncertainties. Ongoing improvements to the measurement system are also discussed.