A Report on Phase 1 of the 5th International Radiocarbon Intercomparison (VIRI)

Abstract

The Fifth International Radiocarbon Intercomparison (VIRI) continues the tradition of the TIRI (third) and FIRI (fourth) intercomparisons (Scott 2003) and operates as an independent check on laboratory procedures in addition to any within-laboratory procedures for quality assurance. VIRI is a 4-yr project, with the first suite of samples (grain) sent out in September 2004 and the second suite (bone) sent out in December 2005. Further stages will include samples of peat, wood, and shell with a range of ages. The 4 grain samples included 2 samples (A and C) of barley mash (20 g for radiometric analysis and 2 mu-g for AMS), a grain (barley) byproduct from the manufacture of Glengoyne malt whiskey. The 2 remaining charred grain samples (B and D) were from excavations at Beth Saida and Tel Hadar, respectively (10 g for radiometric analysis and 4 seeds for AMS) and were provided by Elisabetta Boaretto of the Weizmann Institute. Consensus values for samples A and C are 109.2 (standard deviation [1 sigma] = 2.73) and 110.6 pMC (1 sigma = 2.48), and 2805 (1 sigma = 162.7) and 2835 BP (1 sigma = 190.8) for samples B and D, respectively. Sample A is a new sample that was collected in 2001, while sample C was used in the FIRI trial as samples G J (consensus value 110.7 pMC) and was collected in 1998. The expected ages (on archaeological grounds) of samples B and D are 2800 BP and 2850-2900 BP, respectively. The second suite of samples comprises bone, ranging in age from Medieval to close to background, and was distributed in December 2005. Samples for both radiometric and AMS laboratories include E: mammoth bone (>5 half-lives); F: horse bone (from Siberia, excavated in 2001); and H, I: whalebone. Finally, sample G (human bone) was only for AMS laboratories. Some of the issues related to using bone in a laboratory intercomparison will be discussed.