The carbon isotopic analyses reported here covers the period since the last list (Haynes et al., 1967) until summer 1969. All results relating to secular C14 fluctuations in atmospheric CO2 are now published separately (Damon et al., 1970). Sample preparation and counting procedures remain essentially unchanged since completion of our conversion to CO2 in 1960. All δC13 values are reported relative to PDB and all C14 dates, unless otherwise noted, are based on the 5568 year half-life, but are not corrected for C13 content. 0.95 NBS oxalic acid activity is our routine standard periodically monitored for isotopic fractionation.

This list includes mainly the results of datings done from 1967 to 1969. Methods are essentially the same as those described in Radiocarbon, 1966, v. 8, p. 46–53, 1967, v. 9, p. 38–42, and 1969, v. 11, p. 15–21. Samples synthesized to benzene and counted by liquid scintillation spectrometry. Age calculations are based on 95% of the activity of the NBS oxalic acid standard and computed from the Libby half-life of 5570 yr and reference A.D. 1950. The error listed is the one-sigma statistical counting error. Most samples were counted for 2000 to 3000 min. HCL and NaOH pretreatments were applied to samples as required.

This date list was compiled by the Institute of Geological Sciences (U.K.) incorporating data supplied under contract by Dr. 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 standard error is given as a standard deviation of 1σ. Correction for C13/C12 has not been made. This is the first of a series of annotated lists of C14 dates of British and overseas material in course of preparation by the Institute.

The method used was described in R., 1968, v. 10, p. 29–35. The counter is the same (M.B.L.E. Houtermans and Oeschger) but the electronic apparatus is new; all is transistorized and the installation operates in preset time. The counter is filled at a pressure of 600 to 1000 mm Hg; sample, modern reference, and background are counted at the same pressure and reduced to standard conditions: 760 mm Hg, 20°C. Atmospheric pressure and temperature are measured at each filling. Samples are counted for 20 hours at one month intervals and a third time if measurements do not agree within two standard deviations. Age calculations are based on a contemporary value equal to 0.95 of activity of NBS oxalic acid standard and 5570 yr for the half-life of C14, 1950 used as reference year. Errors quoted include the standard deviations of the count rates for unknown sample, modern and background; no corrections are made for isotopic fractionation.

The I.V.I.C. laboratory continues operation using liquid scintillation spectrometry with synthesized benzene. A plastic-glass counting vessel contains 3 ml benzene, 1 ml commercial toluene, and concentrations of 0.4% PPO and 0.01% POPOP as scintillators. Background is 6.9 cpm and activity of the modern standard, 95% of the activity of the NBS oxalic acid, is 21.4 cpm. In the age calculations, 5568 years is taken for the half-life of C14 and quoted errors are one standard deviation arising from the random nature of the radioactive disintegration process. Uncertainties in the half-life are not included nor are variations in the deposition rate of stratospheric radiocarbon and dilution by industrial use of fossil fuels. A.D. 1950 is employed as the reference year in the B.P. (before present) notation of ages.

The following list comprises measurements made during 1969–70. The method is essentially the same as previously described, using a 0.6 L proportional gas-counter at 3 atm CH4 pressure. Ages are calculated with a half-life of 5570 yr and quoted with 1σ experimental error. Descriptions and comments are based on information supplied by the submitters.

The Radiocarbon Dating Laboratory of the Department of Geology, University of Lyon, is going on with work since its foundation in 1965, in the basement of the Nuclear Physics Institute.

Radiocarbon, Ltd. is a privately owned laboratory designed to provide quality service to the archaeologic and geologic communities. Operations began in 1969 using standard techniques for preparation, conversion to CO2, and purification of samples prior to counting. A sample is counted as CO2 in each of two identical proportional counters of volume 2.2 L, built on the design of östlund and Engstrand (1963); each counter has its own multi-anode guard ring, and is housed in a common shield of iron 8 in. thick.

The following list includes samples dated in 1968 and 1969. Wood dating from A.D. 1850 ± 10 yr is used as contemporary reference standard. Background sample is synthesized from anthracite or shungite. All radiocarbon dates were calculated with C14 half-life of 5568 ± 30 yr. All dates are calculated from the year 1950.

Given below are the dates of archaeologic and Quaternary samples measured by the proportional counting of methane gas. Details of the techniques used were published earlier (Agrawal et al., 1965).

Radiocarbon measurements in this list were made from Sept. to Dec., 1968. They are based on acetylene counting in an Oeschger-Houtermans-type proportional counter (1 L) at pressure 1 atm. All data are based on duplicated measurements. For calculation of ages, 95% activity of NBS oxalic acid is used as the modern standard and value of 5570 + 30 years is used for the half-life of C14. Dates are expressed in years B.P. (before A.D. 1950). Error corresponds to 1σ deviation of sample net counting rate as well as modern standard and background. Details of procedures are given in previous reports (R., 1968, v. 10, p. 144–148; 1969, v. 11, p. 509–514)

The C14 measurements reported here were made in this laboratory between January 1969 and July 1970. Details of our apparatus, sample preparation, and measuring procedure were described in R., 1968, v. 10, p. 144–148. A change has been made since January 1969: strontium carbonate is reduced to strontium carbide with a mixture of 60g of SrCO3 to 40g of Mg-powder (<200 mesh) instead of 60g of SrCO3 to 50g of Mg-powder (<50 mesh).

The dating equipment in the Palaeoecology Laboratory remains essentially as described in R., 1970, v. 12, p. 285–290, and the operating conditions as described in R., 1970, v. 12, p. 291–297. Small samples, however, have been counted at a filling pressure equivalent to 152 cm Hg at 20°C. Charcoal samples pretreated by nitration have been treated as described in R., 1970, v. 12, p. 285–290. Other charcoal samples have been pretreated using the following technique developed by P. Q. Dresser: samples are washed in 5% sodium hydroxide; this is followed by treatment in a solution composed of 8% potassium permanganate and 10% sulphuric acid, at 80°C for 20 mins, to remove residual rootlets and organic matter. Unless specifically stated, the samples have been collected by the authors and other members of the Laboratory: M. G. L. Baillie, P. Q. Dresser, Adelaide Goddard, and I. Goddard. Where a sample has been collected for a specific research project the collector's initials are given. Routine operation of the dating apparatus has been carried out by Mrs. Marilyn Carse and Mrs. Florence Qua to whom we are much indebted.

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 routine processing and measurement of samples in our Radiocarbon Laboratory began early in 1970 following a one-year testing period during which standard samples (anthracite and NBS oxalic acid) as well as samples of known age were prepared and measured. Our system is based on the studies of de Vries and Barendsen (1953), Fairhall et al. (1961) and Olson and Nickoloff (1965). However, several modifications of the cited methods were introduced and are briefly discussed below. A detailed description of the whole system will be published elsewhere (Srdoč et al., 1970).