Presented below are dates from some important archaeologic and Quaternary sites. For the first time, a large number of dates have been reported here on the eustatic changes on the Eastern Indian coast. All dates are based on τ1/2 — 5568 yr; to convert the radiocarbon dates for archaeological samples into ad/bc scale, 1950 has been used as base year as per resolution passed at the Ninth International Radiocarbon Conference, San Diego, 1976. The dates are not corrected for 13C fractionation.

Most of the 14C measurements reported here were made between October 1975 and October 1976. Equipment, measurement, and treatment of samples are the same as reported previously (R, 1968, v 10, p 36-37; 1976, v 18, p 290).

This list contains all analysis completed since the first list (R, 1975 v 18, p 205).

The following list includes samples dated in 1975. The measurement of 14C activity was performed with 1-channel and 2-channel scintillation devices. Special attention was paid to the decrease of the background. The effectiveness of the measurement is ca 50% (Punning, Rajamäe, 1975). The “enriched standard” (Alekseejev et al, 1971) has been used as a contemporary reference standard of modern carbon. Age calculations are based on the 14C half-life of 5568 ± 30 yr, with 1950 as the standard year of reference. All samples are calculated to ± 1σ with respect to sample, standard and background after counting times of at least 2800 minutes. 13C/12C measurements and corrections have not been made for these samples.

Experimental procedures and calculation remain almost as previously described in R, 1977, v 19, p 326-331. The only difference is in the counting equipment. We now use a Beckman LS-230 counter where samples are counted for a total count of about 30,000.

The following radiocarbon measurements are a partial list of projects and samples dated since January 1975. The technique used is described in R, v 16, pp 402-408 and R, v 18, pp 210-220. Dates are calculated using 14C half-life of 5568 yr and errors are reported as one-standard deviation.

Radiocarbon, Ltd moved its laboratory facilities from Spring Valley, New York to Lampasas, Texas in the summer of 1974. This date list represents all results obtained at the Spring Valley location for which sample data have been received, and which have not been reported previously.

This list of measurements includes most of the geologic samples dated in this laboratory since the publication of our last list (R, 1974, v 16, p 252-268).

The following dates are a partial list of archaeologic and geologic samples measured since spring of 1976. The method used is described by (Stipp et al, 1976). Errors reported are one standard deviation and include only the counting errors on the unknown sample, background, and modern standard. No corrections have been made on these dates. Sample descriptions and comments are based on information supplied by the submitters.

Procedures and equipment of the laboratory have been described in previous date lists. 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 samples are treated with dilute HCl instead of H3PO4.

A radiocarbon dating system has been established at the Department of Geology and Geophysics, Yale University. Liquid-scintillation counting of benzene described by Noakes et al (1965) and Polach and Stipp (1967) is used. The operation of the original Yale Radiocarbon Laboratory, based on counting CO2 gas, was suspended in 1969. The present facility is operated as part of the geochemical laboratories of the Department of Geology and Geophysics. The operation is small, geared to solving geochemical problems, through the use of radiocarbon as a dating tool and as a natural tracer in combination with other geochemical parameters. The facility will collaborate on significant archaeologic and geologic problems. However, it will not be a facility to which samples are submitted routinely. We believe that commercial facilities and other laboratories dedicated to such kinds of operation are better suited to handling such diversity and volume of samples.

A radiocarbon laboratory at the US Geological Survey Western Regional Headquarters in Menlo Park, California was established in temporary rooms in March, 1976. In August, 1976 the laboratory was dismantled and moved into a new building that was designed specifically for the facility. This list contains results of operations in the temporary laboratory, which was located in the basement of a two-story building. The counter shield was 15cm lead and 5cm borated paraffin with an additional 5cm of lead above the counters. The anticoincidence ring consisted of copper tubes, 5cm in diameter, mounted around a copper tube with an inside diameter of 15cm. Installed in the anticoincidence ring were the four sample counters, whose characteristics are shown in Table 1. The counting electronics unit, which is designed to service five sample counters, follows the design of Gulliksen (1972) in most respects. The sample counters were constructed of copper and quartz; their design is described in detail by Robinson (1977). The CO2 counting gas was purified by recirculation over copper and silver at ca 450°C. Wood samples were typically pretreated by leaching for 24 hours alternately in 1N sodium hydroxide and hydrochloric acid solutions at 70°C.

This list reports 14C measurements completed between August 1973 and November 1975. Other projects completed in that period will be reported later. Age calculations are based on 14C half-life of 5568 yr and modern standard of 95% NBS oxalic acid, supplemented by tree rings of pre-industrial wood from a log cut in the 1850's (Tx-540; R, 1970, v 12, p 249). Deviations reported are based on counting statistics of sample, background, and modern, and are ± 1σ, except that when sample count approaches either modern or background, 2σ limits are reported. Unless noted, 12C/13C measurements were not made and results are not corrected for 13C fractionation. The laboratory uses liquid scintillation counting of benzene, with Li2C2 and vanadium-activated catalyst in preparation; chemical yields range between 95% and 99%. Three counters are employed: a Packard Tri-Carb Model 3002, and 2 Beckman LS-230 spectrometers obtained through a grant from the National Science Foundation.

The following list contains dates of samples measured since our previous list (R, 1975, v 17, p 149-155). As before, age calculations are based on the Libby half-life 5570 ± 30 yr and reported in years before 1950. The modern standard is 0.950 of the activity of NBS oxalic acid.

The following radiocarbon measurements are a partial list of geologic samples dated since September 1975. The technique used is described in R, v 18, p 210-220. Dates are calculated using a 14C half-life of 5568 yr and errors are reported as one standard deviation. This includes only the counting errors on the sample, background and modern standard.

This list contains the results of some measurements made between 1968 and 1974. Samples were counted in the form of acetylene gas, as previously, and ages were computed on the basis of the Libby half-life, 5568 ± 30 years. The error listed, always larger than the 1σ statistical counting error commonly used, takes into account variable laboratory factors but does not include external (field or atmospheric) variations or fractionation.