The present list contains dates of samples measured since our previous list (R., 1971, v. 13, p. 135–140). As before, age calculations are based on the Libby half-life 5568 ± 30 yr, and reported in years before 1950. The modern standard is 0.950 of the activity of NBS oxalic acid, giving a net counting rate of 21.68cpm. The background count is measured by a series of inactive samples such as marble, anthracite, petroleum coke, and old natural methane. Background count of these samples give a mean value of 6.05cpm. It is observed that marble always gives the highest value of background count while natural methane gives the lowest. Results, however, are within ± 1 σ of the mean value.

This series reports some of the measurements made since publication of the previous list. Equipment and methods remain as described in Saskatchewan II (R., 1960, v. 2, p. 73). The laboratory operates now commercially, administered by the Saskatchewan Research Council under the direction of A. A. Rutherford.

The dating equipment and operating conditions remain essentially as previously described. This list includes some small samples counted at a filling pressure equivalent to 76cm Hg. at 20°C. Carbon isotope ratios were obtained and calculated as described (R., 1973, v. 15, p. 212). All samples are from Ireland.

The dating equipment and operating conditions remain essentially as previously described. Samples in this list were counted at filling pressures equivalent to either 152 or 380 cm Hg at 20°C. Pretreatments are as given in previous lists unless otherwise specified. All wood samples were treated with sodium chlorite and dilute HCl to leave a cellulose-rich residue. Pine wood was in some cases extracted with petroleum spirit in a Soxhlet apparatus before this treatment, to remove resins.

Radiocarbon dates obtained since December, 1970, are summarized here. Procedures and equipment have been described previously (R., 1966, v. 8, p. 522). 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.

This report includes radiocarbon dates obtained since December 1971. Procedures and equipment have been described previously (R., 1966, v. 8, p. 522).