A simple procedure for the conversion of 14C NBS oxalic acid standard to benzene without direct combustion or wet oxidation is reported. Fractionation in the synthesized benzene was not detected.

The carbon isotope analyses reported here include all radiocarbon dates run on packrat middens in the United States and Mexico by the Arizona radiocarbon laboratory through October 1977. All samples described below report dates by CO2 (0.5 or 2.0L) counting. Age calculations are based on a 14C half-life of 5568 years, using 0.949 NBS oxalic acid as the modern value. Errors, based on counting statistics, are quoted to ± 1δ; infinite ages quoted to — 2δ.

The following list contains most of the measurements made during 1977, since our last list (R, 1977, v 19, p 383-388). The laboratory procedures used were those outlined in the previous date lists (R, 1976, v 18, p 151-160; R, 1977, op cit). Dates are calculated using 14C half-life of 5568 yr and errors are reported as one-standard deviation. The collagen extraction follows Longin (1970).

This list includes all measurements made between 1969 and 1973 that represent natural samples. Physical and chemical treatment of samples and counting technique remain as previously reported (R, 1973, v 15, p 469-478). Calculations of dates are made with the radiocarbon half-life of 5568 ± 30 years; plus or minus numbers quoted herein are the standard errors for the counting of radioactive disintegrations.

In this date list we have included most of the archaeologic samples dated in this laboratory since publication of our last date list (R, 1977, v 19, p 188-228).

Presented below are dates from some important archaeologic and Quaternary sites. All dates are based on τ ½ = 5568 yr; to convert the radiocarbon dates for archaeologic samples into ad/bc scale, 1950 has been used as base as per the resolution passed at the Ninth International Radiocarbon Conference, San Diego, 1976. The dates are not corrected for 13C fractionation. All the dates older than 10,000 yr have been given with 2σ errors. Due to uncertainty about the contribution of the biogenic carbon in caliche (CaCO3) samples, the dates represent apparent and not true ages.

This list reports certain 14C measurements completed by November 1977; other projects completed by this time will be reported later. Age calculations are based on 14C half-life of 5568yr 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. Our 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 LS320 spectrometers obtained through a grant from the National Science Foundation.

The following radiocarbon dates are a partial list of samples measured since March 1977. The techniques used are the same as reported in R, v 16, p 402-408, and modified in R, v 18, p 210-220, with the following exception. A third liquid scintillation counter (Beckman LS-100) has been added and the shortened, low-K glass-counting vials have been replaced with teflon vials of Noakes (1975) design. Backgrounds on the counters were thus reduced from 9.1 cpm, 8.8 cpm and 4.9 cpm to 3.8 cpm, 3.5 cpm and 2.8 cpm, respectively, with an attendant small increase in efficiency.

This list contains the results of some measurements made between 1966 and 1975, and includes some earlier unpublished dates. Samples are counted in the form of acetylene gas, as previously, and ages computed on the basis of the Libby half-life, 5568 ± 30 years. The dates have not been corrected for fractionation by making a 13C measurement. The error listed, always larger than the one-sigma statistical counting error commonly used, takes into account possible fractionation in the laboratory and in nature and variability experienced with replicate samples. We thank Linda Wilt for helping in the preparation of the manuscript and Charles Oman for his technical assistance.