The following list consists of dates for archaeologic and some geologic samples, mostly measured from January 1978 to December 1979. The dates were obtained by liquid scintillation counting of benzene using the laboratory procedures outlined in previous lists (see, eg, BM-VIII, R, 1976, v 18, p 16). The dates are expressed in radiocarbon years relative to ad 1950 based on the Libby half-life for 14C of 5570 yr, and are corrected for isotopic fractionation (δ13C values are relative to PDB). No corrections have been made for natural 14C variations. The modern reference standard is NBS oxalic acid (SRM 4990). Errors quoted with the dates are based on counting statistics alone and are equivalent to ± 1 standard deviation (± 1σ). Dates in this list reported to submitters or published elsewhere before the introduction of the new guidelines for rounding of computed figures have deliberately been left unrounded. From BM-XV onwards all BM dates will be rounded before publication in conformity with the recently recommended procedures (R, 1977, v 19, p 362). Descriptions, comments, and references to publications are based on information supplied by submitters.

The following list consists of dates for archaeologic and geologic samples mostly measured over the period from January 1980 to June 1981. The dates were obtained by liquid scintillation counting of benzene using the laboratory procedures outlined in previous lists (see, eg, BM VIII, R, 1976, v 18, p 16).

The following list includes 14C measurements of geologic samples, the majority of which pertain to sea-level variations, and of archaeologic samples mainly from France, West Africa, and South America. Most of the dates were measured between 1972 and 1973 when installations were not modified. The technique used is described in Radiocarbon, 1972, v 14, p 280–320. Dates were calculated using the 14C half-life of 5568 years; modern standard is 0.95 of the NBS oxalic acid. Reported errors are one standard deviation for 2000 minutes measurements.

The SFU Archaeology Department has constructed a small radiocarbon dating facility to serve its own needs and, to the extent that time is available, the needs of other archaeologists and earth scientists. All dates reported here were processed by our laboratory from October 1979 to September 1980. The 14C measurements are made using conventional techniques for liquid scintillation counting of benzene. The samples are burned in a Phonon Mark IV combustion bomb and the resultant CO2 is purified and converted to Li2C2 using a reaction vessel based on the design of Polach, Gower, and Fraser (ms). Acetylene is formed by hydrolysis with distilled H2O which has been aged for a minimum of three months. The acetylene is trimerized to benzene with the Mobil Durabead I catalyst. The conversion efficiency of CO2 to C6H6 is typically 95%. Gas chromatographic analysis of typical samples of the synthesized benzene indicates 99.8% purity with toluene produced in trace amounts.

Results of extensive and systematic radiocarbon dating of tufa samples and associated materials (wood, plants, moss, and peat) are presented in this paper. Samples were collected in Plitvice Lakes National Park, Central Croatia, Yugoslavia, where intensive precipitation of tufa has taken place over several geologic epochs in a typical Karst area. Problems associated with radiocarbon dating of tufa are discussed in a previous paper (Srdoč et al, 1980). The authors concluded that dating of tufa is feasible and reliable, at least in the specific case of Karst regions, where retention of groundwater is short. Tufa is precipitated as a result of decomposition of groundwater bicarbonates due to loss of CO2, usually in waterfalls and cascades, and it is practically contemporaneous with living organic material. However, radiocarbon activity of modern tufa is lower than that of organic material due to dissolution of inactive carbonates (limestone) in groundwater. The initial activity of groundwater depends on the geology and vegetation of the area and it is widely discussed in the literature (Geyh, 1973). The initial activity, Ao, of tufa could be easily measured on recent samples, had not bomb-test contamination upset the equilibrium. Namely, while the atmospheric CO2 and living matter responded relatively quickly to the injection of radiocarbon in the atmosphere, groundwater and, consequently, tufa showed a much slower and damped response. Therefore, we have based our estimation of the initial activity of tufa on measurements of samples of known age collected before the bomb-test era. An average value of the initial activity equal to 85% of modern has been obtained which is in accordance with data for groundwater activity in similar areas. Consequently, all radiocarbon ages of tufa samples in this paper are based on the Libby half-life of 14C (5568 years) and the initial radiocarbon activity equal to 85% of modern. The modern standard is 0.95 of the activity of NBS oxalic acid. Errors quoted are based on counting statistics only and do not include uncertainties in 14C half-life and in initial activity. The latter may introduce much larger errors, up to ± 1000 years, depending on the sampling site, as explained in the following sections. Whereas radiocarbon dating of Holocene tufa beds give reliable ages within the above specified errors, radiocarbon dating of old tufa beds is still questionable. Intrusion of minute quantities of modern calcareous material renders the ages of old (∼30,000 yr) tufa useless. Research on measuring the age of old tufa deposits by other methods is in progress.