C14 measurements of archaeologic and geochemical samples using sample synthesized benzene in a Beckman LS-100 liquid scintillation spectrometer are reported. Rather high background counting rates of ca. 8 to 9 cpm and counting efficiency of ca. 45 to 48% for 4 cc counting vial of potassium free glass are observed. The counting vial (total volume of 10 cc) is supported by an aluminum bar for geometry control. Background and standard counting rates measured during the past 17 months are listed in Tables 1 and 2, respectively. Slight seasonal variations were observed.

C14 dates reported below were obtained mainly at the end of 1968 and during 1969 on archaeologic and geologic samples. Techniques of measurement used are unchanged. Since 1968, 4 complete routine sets have been running, each equipped with a 1 L CO2 proportional counter. One is made of stainless steel with a background of 2.70 cpm at pressure 1 atm and the others are of OFHC copper with a background of either 1.10 or 1.30 cpm for a corresponding pressure of, respectively, 1 or 2 atm. For age calculation, 95% activity of NBS oxalic acid is used as the modern standard and the value of 5570 ± 30 years is used for the half-life of C14. Dates are expressed in years b.p. (before a.d. 1950).

Operation of counting systems and preparation of results remain as described previously by Baxter et al. (1969), and Ergin et al. (1970).

The following list presents results obtained during 1970-1971 and is a continuation of research of which data have been pub. previously (Baxter et al., 1969; Ergin et al., 1970; Baxter and Walton, 1970; Harkness and Walton, 1972; Ergin et al., 1972). The major research efforts at Glasgow are aimed at evaluation of (a) natural annual C14 levels and (b) burdens and residence times of artificial C14 in the environment and human tissues. The results of these studies are presented as δC14 and Δ values based on age-corrected activities, although this correction is very small. The errors quoted are counting uncertainties only, expressed at the 1σ level. Pretreatment procedures are outlined in the text and analytical methods are essentially unchanged. Gas proportional counting of both CO2 and CH4 is employed in 2.6L and 0.5L detectors, respectively. Mass spectrometric analyses are performed to a precision of 0.1‰ (± 2σ) on a V.G. Micromass 602B stable isotope mass spectrometer.

This date list was compiled by the Institute of Geological Sciences (U.K.) incorporating data supplied under contract by 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 error, based on counting statistics of sample, background, and modern, is given as one standard deviation. Correction for C13/C12 fractionation has not been made.

The current list presents samples measured in the radiocarbon laboratory, Leningrad Branch Inst. of Archaeol., Acad. of Sci., USSR, from July 1967 through June 1969. Ages of 85 archaeologic samples of wood, charcoal, and peat have been determined.

The following list of measurements contains selected results obtained by the La Jolla Radiocarbon Laboratory from November 1966 to July 1971. During the same period 382 measurements were made on tree-ring-dated wood in studying secular variations of the atmospheric C14 level and of the absolute radiocarbon time scale [Suess, 1970a, 1970b]. Results of these measurements are not included here. Also not included are 124 measurements of C14 determinations in extraterrestrial material and results of other occasional investigations will be published elsewhere.

The C14 measurements reported here were made in this laboratory between October 1970 and September 1971. Equipment, measurement and treatment of samples are the same as reported previously (R., 1968, v. 10, p. 36-37; 1970, v. 12, p. 534).

This list includes those samples dated between December 1968 and July 1971. Samples before SI-617 were completed before the laboratory was dismantled in April 1969 for renovations in the Smithsonian Institution Building. Samples beginning with SI-617 were dated after December 1970, following re-establishment of the laboratory in new quarters.

Preparations to establish a radiocarbon dating laboratory at the University of Sydney were made in 1970 in the Department of Physical Chemistry, to support Ph.D. studies and to supplement existing dating services in Australia to the archaeologic and geologic communities.

This date list covers most of the datings made during 1968 to 1970. Each sample is measured in one of the two counters described previously (R., 1970, v. 12, p. 205-237).

The radiocarbon laboratory in the Oceanography Department at Texas A&M University was established primarily for the examination of seawater samples, although other types of samples have been run. Emphasis has been placed on seawater samples of the Gulf of Mexico and adjacent areas. Most of the samples examined have been inorganic carbon, but some organic-carbon samples are being run, mainly wood and charcoal whose ages have been determined previously. More samples of known age will be run as a further check on the reliability of experimental methods and procedures.

The Radiocarbon Dating Laboratory of Tehran University Nuclear Centre began operation in autumn 1970. Benzene synthesis and liquid scintillation counting was chosen as the best method for processing a large number of archaeologic specimens most of whose ages are less than twice the half-life of C14. Advantage of benzene synthesis; ease of chemical processing light transfer properties, lack of isotopie fractionation and radioactive contamination, removal of radon, and improbability of cross-contamination, have been discussed (Noakes et al., 1964; Noakes, Stipp, and Hood, 1964; Kowalski, 1965).

This laboratory is now a branch of the Texas Memorial Museum of the University of Texas at Austin. This list reports C14 measurements made in projects completed between October 1969 and August 1971. A number of major projects are still in progress and are to be reported later. Age calculations are based on C14 half-life of 5568 yr and modern standard of 95% of NBS oxalic acid. 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. Except where noted, C12/C13 measurements have not been made, and results are not corrected for C13 fractionation. The laboratory uses liquid scintillation counting of benzene, with Li2C2 and vanadium-activated catalyst in preparation; chemical yields average 88%. The counter is a Packard TriCarb Model 3002.

The following list of dates is compiled from samples prepared since publication of our last date list (R., 1971, v. 13, p. 468-474). The counting equipment and operating procedures are the same. Ages are quoted with a lσ counting error which includes statistical variation of the sample count as well as for the background and standard, using a.d. 1950 as the reference year and 0.95% NBS oxalic acid for C14 dating as the standard. The half-life value used is 5570 years.

Measurements have continued with the same proportional counter system, sample pretreatment procedure, methane preparation and measurement, and calculation using a half-life of 5568 ± 30 yr as described previously (R., 1970, v. 12, p. 298-318). Uncertainties quoted are single standard deviations originating from standard, sample, background counting rates and half-life. No C13/C12 ratios were measured.