The present date list contains only details of C14 measurements on sites selected for archaeomagnetic study. Except where otherwise stated in the text, all samples were collected in 1970 or 1971 during fieldwork by one of the authors (M.B.), and were pretreated with hot 2N HCl to remove any possible contamination by pedogenic carbonate. Benzene samples were prepared using updated synthesis techniques (Polach et al., 1972) and measurements of C14 activity were made on two Beckman LS-200 liquid scintillation spectrometers following automatic cycling procedures described previously (Polach, 1969). Samples ANU-677-697 were counted on the spectrometer which has been in use since 1968 (LS-1).

Continuation of radiocarbon measurements, mainly on ground water, soil, and subhydric sediment samples. Sample preparation was described earlier (Scharpenseel and Pietig, 1969).

The measurements presented below were made during 1970–71 by techniques described in R., 1968, v. 10, p. 246, and 1970, v. 12, p. 87. Errors associated with the de Vries effect and the uncertainty of the half-life are not included. In November 1971 a new low level, quartz-lined 1/2L counter designed by M. Stuiver was put into operation. It has allowed routine measurements with the samples representing 500mg to 1g pure carbon.

This date list was compiled by the Institute of Geological Sciences (U.K.) incorporating data supplied under contract by E. Welin, Radioactive Dating Laboratory, Stockholm. Unless otherwise stated, age figures are in C14 years before a.d. 1950. The half-life of C14 is taken as 5568 years and the error, based on counting statistics of sample, background, and modern, is given as one standard deviation. Correction for C13/C12 fractionation has not been made.

This list includes the results of datings made during 1970–71. The methods of measurements are the same as described in R., 1971, v. 13, p. 29–31.

The samples reported in this date list were processed during 1970. Alter preliminary sample treatments including carbonates and rootlet removal, a complete benzene synthesis was made. This liquid serves as the solvent in a liquid scintillation spectrometer, using a modified 4cc: counting vessel; 2.42g of carbon are counted with a 64% efficiency. The background is constant at 6.8 cpm.

The following list of dates includes most of the samples processed from 1968 to 1972. Proportional counting is used and the counting gas is CO2 at constant filling pressure of 740mmHg at 22°C (Thommeret et al., 1969). Samples are counted at least twice on two different counters and errors quoted are averages of standard deviations obtained on each counting.

The C14 dates given below have been obtained by counting CO2 at 2 atm pressure in a 1 L proportional counter. Details of procedure are given in our previous list (R., 1970, v. 12, p. 187–192). Radiocarbon dates in this list are based on 95% of activity of NBS oxalic acid as the modern standard and were calculated using 5570 yr as the half-life of C14. Errors quoted with the dates are standard deviation originating from the statistical nature of radioactive disintegration process. Results obtained during 1970 and 1971 are described here.

The following list of determinations is compiled from samples prepared since publication of our last date list (R., 1969, v. 11, p. 137–149) and includes sample measurements through July, 1970. The Radiocarbon Laboratory was dismantled and transported to Halifax, Nova Scotia, where it will resume operation as the Dalhousie University Radiocarbon Dating Laboratory.

This date list includes most of the archaeologic and geologic samples dated in this laboratory since publication of our last date list (R., v. 12, p. 577–589), as well as some samples which had previously been dated, but lacked the sample information necessary for publication. Known-age samples, completed in this time period, will be reported elsewhere. The b.p. ages are based upon a.d. 1950, and have been calculated with the half-life value of 5568 yr. All samples were counted at least twice for periods of not less than 1000 minutes each. Errors quoted for each sample are derived from the measurement of the sample, the background, and of several counts of our mid-19th century standard oak sample, but do not include the half-life error. All samples were pretreated with 3N HCl, and some, where noted, were given additional pretreatment with 2% NaOH for the removal of possible humic acid contaminants.

During the last few years, we have set up the benzene scintillation method in our laboratory. C14 activity measurements are now carried out with both liquid scintillation and CO2-proportional counters. Chemical apparatus for benzene synthesis and a liquid scintillation spectrometer for low-level counting were built and are described below.

This list includes samples completed to July, 1972. All samples are counted for at least 2500 min., and X2 analyses are made on 100-min. print-outs. Errors quoted are 1σ, derived from sample, background, and NBS oxalic acid standard measurements, adjusted where appropriate for small-sample dilution.

Measurements have continued with the same proportional counter system, the same procedure in sample pretreatment, methane preparation and measurement, and the same age calculation using a half-life of 5568 ± 30 yr as described previously (R., 1970, v. 12, p. 298–318).

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.