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.

The following list comprises results obtained during 1970 from both the 1 L and 6 L counters. Results are not corrected for C13 fractionation. Errors quoted refer only to the standard deviation calculated from a statistical analysis of sample and background count rates and the Libby half-life of 5570 ± 30 yr. Pretreatment has been continued as described previously (R., 1969, v. 11, p. 263). In cases where sample size was insufficient for full pretreatment, details of the necessary deviations accompany the result.

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.

Dates listed below are based on measurements made from June 1968 to May 1970 by the liquid scintillation technique using benzene. In general, the experimental procedure is as described previously (Barker, Burleigh, and Meeks, 1969a) with a few changes in detail. Data are now processed by computer using a comprehensive Algol program written by Andrew Barker, King's College, Univ. of London. There is no need to standardize on any particular sample weight and, as the benzene synthesizer can also deal with samples in the range up to the equivalent of 9 gm of carbon in a single synthesis, the amount of sample available is now less critical. However, for older material, a minimum of 1 gm of carbon is required. Another factor contributing to efficiency of operation is the “bomb” technique for sample combustion (Barker, Burleigh, and Meeks, 1969b), also mentioned in the previous date list. Finally, during 1969, an MS20 double collection mass spectrometer was acquired and all dates (but not all those in this list) are now corrected for isotopic fractionation.

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.

Radiocarbon measurements, mainly on soil and water samples have been continued. Sample preparation is carried out following methods described by the authors elsewhere (Scharpenseel and Pietig, 1968/69; 1970a, b).

This list consists mainly of dates obtained from analysis during 1967 and 1968 of archaeologic and geologic samples. The last section deals essentially with climatic, palynologic, and sea level variation problems. All measurements of atmospheric CO2 made periodically from 1962 until end of 1970 are also published here. In agreement with international convention, all dates have been calculated on the basis of the C14 half-life of 5568 years and 95% of NBS oxalic acid as the modern reference year.

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.

During the past year, 1969-1970, both the 2-L (Dyck and Fyles, 1962) and 5-L (Dyck et al., 1965) counters were routinely operated. A 1-L counter was finally constructed with acceptable characteristics (see description below) and was operated in July in place of the 5-L counter. The 2-L counter was operated exclusively at 2 atm. The 5-L counter was operated at 1 atm, except for October and November, 1969, when it was operated at 4 atm. The 1-L counter was operated at 1 atm.

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.

This list contains data obtained during 1970. Age calculations are based on 95% of NBS oxalic acid standard activity with modern value A.D. 1950. Results are calculated using the Libby half-life and are given in the B.P. scale. They are not corrected for δC13 variations. Errors correspond to 1σ variation of sample net counting rate including statistics of modern standard and background.

The C14 measurements reported here were made in this laboratory between October 1969 and September 1970. The measuring technique and equipment, and the treatment of samples are the same as reported previously (R., 1968, v. 10, p. 36-37; R., 1970, v. 12, p. 534).

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.

The following list comprises selected measurements obtained by counting methane at 3 atm pressure in a 0.6 L stainless steel counter. Sample preparation, counting procedure, and calculation method are described in previous lists. Dates are reported in terms of the Libby half-life. The quoted errors are the experimental standard deviations including uncertainty on samples and standards.

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.

This date list includes those series of samples completed in this laboratory as of December 1970. The B.P. ages are based upon A.D. 1950, and are calculated with a half-life value of 5568 yr. All samples were counted at least, twice for periods of not less than 1000 minutes each. Errors quoted are derived from measurement of samples, background, and modern-age calibration, but do not include any half-life error. All samples were pretreated with 3N HCI, and some, where noted, were given additional pretreatment with 2% NaOH for the removal of possible humic contaminants.

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).

In 1969 radiocarbon dating facilities were established at the National Physical Research Laboratory of the C.S.I.R. in Pretoria (25° 43′ S Lat, 28° 21′ E Long; alt 1500 m). The counters are situated in an underground room built of selected concrete and covered by ca. 12 m earth. In this room, the nucleonic component of cosmic radiation is practically absent and the meson flux is reduced by a factor of 3.5 as compared to the surface at sea level in Groningen, Netherlands. A neutron monitor which registers 30 cpm on the surface, counts ca. 0.1 cpm in the underground room.