INTERCOMPARISON OF HIGH-PRECISION DELTA-C-14 ANALYSES USING GAS COUNTING AND AMS

We report results of a three-year intercomparison experiment between t he WHOI Radiocarbon Laboratory (now at University of California, Irvin e) and the NSF-University of Arizona AMS Laboratory, The purpose of th is study was to compare high-precision measurements of samples obtaine d routinely using gas proportional counting techniques with results ob tained using AMS techniques. Three sets of annually banded, modern cor al samples were used for the intercomparison. Each sample was acidifie d to CO2 at WHOI and split into two fractions. The larger fraction was converted to acetylene gas and counted at WHOI in quartz, gas-proport ional beta counters. The smaller fractions were converted to graphite and analyzed for C-14 using AMS techniques at the University of Arizon a. Results of the three sample sets are presented. Except for a single outlier, the data from the two laboratories are in good agreement. Of the 13 samples in the third set of the intercomparison, for which a n ew high-intensity ion source was in operation at the Arizona AMS labor atory, agreement of results is excellent. This finding indicates that measurements made with precisions of < 3 parts per thousand are reprod ucible at both laboratories.