University of Cambridge Natural Radiocarbon Measurements XII

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Abstract
The dates presented here comprise results obtained since our last list (R., 1973, v. 15, p. 156-164). Pure carbon dioxide prepared from the samples is used to fill copper proportional counters at two atmospheres pressure. The detectors are protected from environmental radiation by a massive lead shield inside which, and completely surrounding the proportional counters, is a high efficiency plastic scintillation anticoincidence screen (Switsur, Hall, and West, 1970). Modern sample gas is obtained from combustion of a.d. 1845 to 1855 rings of an oak tree grown near Cambridge, felled in 1950. Background samples are prepared from Welsh anthracite or Connemara limestone. The contemporary standard is compared frequently with the activity of NBS oxalic acid international standard. Age calculations are based on the 14C half-life of 5568 years and the uncertainty stated as one standard deviation calculated from the statistical analysis of sample and standard counting rates.

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