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.

The following series of dates contains most of the measurements obtained since our last list. Procedures of measurements and calculation are as previously described (R., 1970, v. 12, p. 353–357).

This list contains most of the unpublished radiocarbon dates measured between 1961 and 1968. Analyses of the C14 content of groundwater are excluded and a number of geologic dates will be included in a later list. Certain earlier analyses performed by H. de Vries and H. de Waard are included, as well as a few results obtained since W. G. Mook assumed responsibility for the laboratory in 1969, to complete series. Descriptions and comments are mainly based on information supplied by the submitters or contained in the publications cited. However, our own interpretation is often given in the comments. Sections I A to D2, II B1, and B2 were mainly prepared by the first author and the rest by the second.

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).

The following list and data presented previously (R., 1970, v. 12, p. 494–495) were obtained to investigate the transport of carbon between man and his environment (Harkness, 1970). These data constitute a study of contemporary variations of C14 concentrations viz., Suess effect and bomb effect, as reflected in the tissues and food chain of the population of the United Kingdom (Harkness and Walton, 1969).

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

The measurements presented in this date list were made in the Radiocarbon Dating Laboratory at Teledyne Isotopes during 1969–70. Samples were analyzed by techniques described in R., 1968, v. 10, p. 246. Methods and references to sample pretreatment are provided in R., 1970, v. 12, p. 87. Errors associated with the age determinations are calculated by combining standard deviations from oxalic acid standard, background, and actual sample data. Samples which approach modern or background are reported with at least 2σ limits. Counting time for calculation of errors of background and standard is the same as that used for the sample. The error associated with the De Vries effect and the uncertainty of the half-life are not included.

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.

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 and the standard error is given as a standard deviation of 1σ. Correction for C13/C12 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.

This list includes the results of datings made during 1969–70. The method is essentially the same as described in R., 1968, v. 10, p. 29–35; 1971, v. 13, p. 29–31.

The following date list includes all samples processed from December 1969 through November 1970 at the Illinois State Geological Survey Radiocarbon Dating Laboratory. The benzene liquid scintillation technique was used, following the method of Noakes, Kim, and Stipp (1965), and Noakes, Kim, and Akers (1967). Detailed sample preparation procedures used in this laboratory have been reported by Kim and Ruch (1969), and Kim, Ruch, and Kempton (1969).

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 following is a list of dates obtained since the compilation of List XIII (R., 1970, v. 12, p. 161–180). The method is essentially the same. Two CO2–CS2 Geiger counter systems were used. Equipment and counting techniques have been described elsewhere (Crane, 1961). Dates and estimates of error in this list follow the practice recommended by the International Radiocarbon Dating Conferences of 1962 and 1965, in that (a) dates are computed on the basis of the Libby half-life, 5570 yr; (b) A.D. 1950 is used as the zero of the age scale; and (c) the errors quoted are the standard deviations obtained from the number of counts only. In Michigan date lists up to and including VII, we quoted errors at least twice as great as the statistical errors of counting in order to take into account other errors in the over-all process.

The following is a list of dates obtained since the compilation of List XIV, and the method is essentially the same. Two CO2–CS2 Geiger counter systems were used. Equipment and counting techniques have been described elsewhere (Crane, 1961). Dates and estimates of error in this list follow the practice recommended by the International Radiocarbon Dating Conference of 1962 and 1965, in that (a) dates are computed on the basis of the Libby half-life, 5570 yr, (b) A.D. 1950 is used as the zero of the age scale, and (c) the errors quoted are the standard deviations obtained from the number of counts only. In Michigan date lists up to and including VII, we quoted errors at least twice as great as the statistical errors of counting, to take account of other errors in the over-all process.

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).

The C14 dates given below are continued from our previous list (R., 1970, v. 12, p. 559–576), and results obtained mainly during 1970 are described. A 2.7 L stainless steel counter and a 3.3 L copper counter are used, yielding background counting rates of 5.5 and 8.5 cpm, respectively, when filled with dead CO2 at ca. 1.8 atm. Dates have been calculated on the basis of the C14 half-life of 5568 yr and 95% of NBS oxalic acid as modern standard.

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.