Radiocarbon dating involves a comparison of the count rate of sample carbon with that of modern reference standard material. To calculate a date the ratio Z must be determined where

The construction and performance of a proportional CO2 counter system is described by which an over-all accuracy is obtained of 1.3‰ after a two-day counting period.

The following list consists entirely of dates for archaeologic samples from the prehistoric flint mining site of Grime's Graves, Weeting, Thetford, Norfolk, England (52° 30' N, 0° 40' E, Natl Grid Ref TL 816898), measured over the period from August 1973 to December 1977,* all the samples having been excavated between 1972 and 1976. The dates were obtained by liquid scintillation counting of benzene using a Model 3315 Packard Tricarb Liquid Scintillation Spectrometer linked to a Hewlett Packard 2100A computer system for on-line processing of counting data (Hall & Hewson, 1977). The laboratory procedures used were those outlined in the two previous lists (R, 1976, v 18, p 16; 1977, v 19, p 143).

This series reports some of the measurements made since publication of the previous list. Methods essentially remain as described in Saskatchewan II (R, 1960, v 2, p 73). The laboratory now joins operation with the National Museum of Canada, Ottawa. The prime purpose is to provide radiocarbon dating service for Canadian archaeologists through the National Museum, although commercial services are available to others as analytical capacity permits.

Experimental procedures and methods of age calculation are as previously described (Gillespie Sc Temple, 1976), except that bc/ad ages are not reported (resolution of 9th Radiocarbon Conference, 1976).

The following radiocarbon dates are a partial list of samples measured since January 1978. The chemical, counting and calculation procedures are the same as indicated in R, v 20, p 000-000.

Measurements have continued with the same proportional counter system, pretreatment procedure, methane preparation and measurement, and calculation, as described previously (R, 1970, v 12, p 298-318). Uncertainties quoted are single standard deviations originating from standard, sample, background counting rates and half-life. No 13C/12C ratios were measured.

Procedures and equipment have been described in previous date lists. Except as otherwise indicated, wood, charcoal and peat samples are pretreated with dilute NaOH and dilute H3PO4 before conversion to the counting gas methane; marls and lake cores are treated with acid only. Very calcareous materials are treated with HCl instead of H3PO4.

The following list contains dates of samples measured since our previous list (R, 1977, v 19, p 465-475). As before, age calculations are based on the Libby half-life, 5570 ± 30 years, and reported in years before 1950. The modern standard is 0.95 of the activity of NBS oxalic acid. Solid sample pretreatment, combustion and counting technique are essentially the same as described in R, 1971, v 13, p 135-140. Groundwater samples were prepared following the procedure adopted by the IAEA (IAEA, 1977). Carbonates and hydrocarbonates from water samples were precipitated by adding saturated barium chloride solution while the alkalinity was adjusted to pH = 8 by adding carbonate-free saturated solution of sodium hydroxide. The precipitation was enhanced by adding iron salts and Praestol as coagulating medium. Carbon dioxide was evolved by acidification of the precipitate and converted to methane. Statistical processing of data has been computerized (Obelić and Planinić, 1975). Sample descriptions were prepared with collectors and submitters. The errors quoted correspond to 1σ variation of sample net counting rate and do not include the uncertainty in 14C half-life.