14C Half-life Research Articles

University of Texas at Austin Radiocarbon Dates VIII

This list reports C14 measurements made in projects completed in the year ending October, 1969, and some measurements for projects still in progress. Age calculations are based on C14 half-life of 5568 years and a 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. The laboratory uses liquid scintillation counting of benzene, with Li2C2 and vanadium activated catalyst in preparation. Chemical yields average 88%.

University of Kiel Radiocarbon Measurements IV

The following dates are samples measured since publication of Kiel III (Radiocarbon, v. 10, p. 328–332). Age calculations are based on 95% of the activity of NBS oxalic-acid standard as modern value of A.D. 1950. Results are calculated with Libby half-life and reported in yr before 1950. Error corresponds to 1σ variation of sample net counting rate as well as modern standard and background, but does not include the uncertainty in C14 half-life and in secular C14 variations. Dates are not corrected for isotopic fractionation.

University of Tokyo Radiocarbon Measurements II

Radiocarbon measurements in the list below were made during the period from Sept. 1967 to Aug. 1968. Our measuring system is based on acetylene counting in an Oeschger-Houtermans-type proportional counter (1 L) at a pressure of I atm. All data are based on duplicated measurements. For calculation of ages, 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. Details of procedures are given in the previous report (Radiocarbon, 1968, v. 10, p. 144-148).

Gakushuin Natural Radiocarbon Measurements VII

This list continues Gakushuin VI (Radiocarbon, 1967, v. 9, p. 43-62), the same instruments and techniques having been employed.Age calculations are based on the Libby half-life of C14, 5570 ± 30 years, and the modern activity given by 0.95 Aox, i.e., 95% of the activity of NBS oxalic acid standard. The errors quoted are the standard deviation obtained from the number of counts only. When observed activity is less than 2σ above background, infinite date is given with a limit corresponding to the activity of 3σ, and when it is greater than 0.95 Aox −2σ, modern date is given with a limit = 0.95 Aox —3σ. For shell samples, dates are computed without any correction for environmental and biological isotopic fractionation.The description and comments are essentially those of the submitters.

Illinois State Geological Survey Radiocarbon Dates I

The radiocarbon dating laboratory of the Illinois State Geological Survey has been established to satisfy a growing need for radiocarbon dates for an active Pleistocene research program. Because of the age and type of material dated, the benzene liquid scintillation counting method is employed in this laboratory. The detailed chemical procedure for converting carbon to benzene has been published by Noakes, Kim, and Stipp (1965) and Noakes, Kim, and Akers (1967); however, the procedures for benzene synthesis and sample counting are briefly explained below to clarify this laboratory's procedure.An organic sample, such as peat, organic silt, or wood, is burned and the CO2 evolved is absorbed in NH4OH. SrCl2 solution is added to precipitate the carbonate, and the solution plus precipitate is boiled and cooled before filtration of SrCO3. The SrCO3 is acidified with dilute H3PO4 to liberate CO2 in a closed system, and the CO2 is converted to C2H2, as reported by Barker (1953). In this method, 2.4 gm of dry packed lithium, obtainable from the Lithium Corporation of America, is used for each liter of CO2 that is converted to C2H2. Trimerization of the C2H2 to form C6H6 is accomplished using a vanadium-alumina catalyst.To the C6H6 synthesized from the sample carbon, 2 cc of toluene containing 100 mg Butyl-PBD, 2-(4-tert-Butylphenyl)-5-(4-Biphenylyl)-1,3,4-Oxadiazole, are added, and this mixture is made to a total volume of 10 cc with spectrograde C6H6. A modified Packard Instrument Co. liquid scintillation spectrometer (Model 3375) is used for measurement of C14 activity.Ages are calculated from a C14 half-life of 5568 years, and the standard deviation (1σ) is based only on counting errors; however, if calculated error is less than 200 years, 200 years is chosen as one standard deviation (1σ).

Riken Natural Radiocarbon Measurements V

The C14 dates given below are a continuation of the work presented in our previous list (Radiocarbon, 1968, v. 10, p. 333-345), and have been obtained by counting CO2 at ca. 2 atm pressure in a 2.7 L stainless steel counter. Results obtained mainly during 1968 are described.Dates have been calculated on the basis of the C14 half-life of 5568 yr and 95% of NBS oxalic acid as modern standard.

Nancy Natural Radiocarbon Measurements II

The following list includes a selected number of measurements made during 1967-1968 in the Natural Radiocarbon Laboratory of the Centre de Recherches Radiogéologiques de Nancy. This list is a continuation of Nancy Natural Radiocarbon Measurements I (Radiocarbon, 1968, v. 10, p. 119-123). The dating method, counting technique, and equipment are described in that list. All measurements were made in a proportional counter with a capacity of 1.16 L, normally filled with CO2 under a pressure of 736 mm Hg. Ages are calculated using a C14 half-life of 5568 yrs with 1950 as reference yr. Modern standard used following samples Ny-118 is 95% of NBS oxalic acid activity. The SC14 mentioned later in the date list are calculated according to Broecker and Olson (1959).

University of Wisconsin Radiocarbon Dates V

The radiocarbon dates obtained since August, 1967 are included in this report. The procedures followed have been described previously (Wisconsin II).The reported dates have been calculated using 5568 as the half-life of C14, 1950 as the reference year. Samples are run at least once in each of two counters at 3 atm pressure for a minimum of 15,000 counts. The standard deviation quoted includes only the 1σ of the counting statistics of background, sample, and standard counts.

University of Kiel Radiocarbon Measurements III

Most of the measurements have been obtained with a 4.5-L CO2 counter (Kiel I). Dates given are not corrected for C13/C12 except Ulmus series. Error corresponds to 1σ of statistical variations of sample net counting rate including variance of reference and background, but does not include the uncertainty in C14 half-life and in secular C14 variations. Half-life is 5570 yr and a.d. 1950 is zero point of b.p. scale.

Washington State University Natural Radiocarbon Measurements I

The College of Engineering Research Division radiocarbon dating laboratory began operating in November 1962 employing a Sharp Laboratories, Inc., CDL-14 system based upon the methane method of Fairhall, Shell, and Takashima (1961).Dates reported herein are calculated using a 5568 yr C14 half-life. The modern standard is taken as 95% of the NBS oxalic acid C14 standard which is converted to CO2 followed by conversion to CH4 in the manner of Fairhall et al. The errors quoted are the 1 σ statistical errors.

Oak Ridge Associated Universities Radiocarbon Dates II

The Radiocarbon Dating Laboratories of the Oak Ridge Associated Universities (ORAU) has previously published radiocarbon dates under the Oak Ridge Institute of Nuclear Studies (ORINS) name. ORINS has recently changed its name to ORAU and its laboratories and programs have accordingly assumed this new name. The ORINS prefix, which previously designated the published radiocarbon dates of this laboratory, will be continued to minimize confusion in the literature.The radiocarbon dating program carried out at this laboratory is primarily concerned with assisting the ORAU Special Training Program in its teaching and research activities. Radiocarbon dates which appear in this paper represent samples submitted from research groups associated with the 41 universities which make up ORAU and by other college and university personnel who do not have access to radiocarbon dating facilities.Carbon samples are chemically synthesized to liquid benzene and their C14 activity determined by liquid scintillation spectroscopy. Samples are first converted to lithium carbide and then to acetylene gas as described by Barker (1953). The acetylene is catalytically trimerized to benzene by a method described by Noakes et al. (1965). Chemical yields for the synthesized benzene routinely approach 90% with no evidence of chemical impurities or carbon isotope fractionation occurring in the chemistry.A Packard Tricarb Model 314 D.C. liquid scintillation spectrometer, which has been modified for low level counting, is used to count the benzene samples. Counting efficiency is 50% when operating at a voltage of 800 with discriminator setting of 100-800-1000. Background count rate is 1.7 c/m with a 5 cc benzene sample. Shielding consists of 4 in. of lead with coincidence and anticoincidence systems.The modern reference standard is 0.95% activity of NBS oxalic acid standard which is 6.82 c/m/g carbon. Ages are calculated on a C14 half-life of 5570 yr as suggested by Godwin (1962). The statistics quoted are compiled as one standard deviation (1σ) of the uncertainty involved in counting background, standard, and sample.

University of Texas at Austin Radiocarbon Dates VI

This laboratory is now a part of the Bureau of Economic Geology, The University of Texas at Austin. The present list reports C14 measurements made in dating projects completed in the year ending November, 1967, and some measurements for projects still in progress. Age calculations are based on C14 half-life of 5568 yr and a modern standard of 95% of NBS oxalic acid. The deviations reported are based on the counting statistics of the sample, background, and modern, and are ± 1σ except that when the sample count approaches either the modern or the background, 2σ limits are reported. The laboratory continues to use liquid scintillation counting of benzene, using Li2C2 and vanadium activated catalyst in preparation, as described in Texas IV and earlier lists. Chemical yields now average 85%.Rightmire's caliche dating (done for an M.A. thesis in the Dept. of Geol.) is the principal project reported in this list; in addition to the research he prepared the samples in our laboratory and wrote the statements which accompany the list. Valastro is in charge of all technical operations in the laboratory, and he and Davis share the administrative responsibilities. Davis, who handles sample screening (with the aid of an Advisory Committee) and archaeological appraisal, compiled the list.

Riken Natural Radiocarbon Measurements IV

The C14 dates given below are a continuation of the work presented in our previous list (RIKEN III), and have been obtained by counting CO2 at ca. 2 atm pressure in a 2.7 L stainless steel counter. Results obtained mainly during 1967 are described.Shell samples were treated with 1% HCl to remove the outer 10%. Calcareous deposits on the surface, when observed, were removed by mechanical means.Dates were calculated on the basis of the C14 half-life of 5568 yr and 95% NBS oxalic acid as modern standard. No correction was applied even for fresh water shell samples.

Louvain Natural Radiocarbon Measurements V

The measurements reported in this list were made in the Louvain C14 dating laboratory in 1966. Sample preparation, counting procedure and calculation method are described in the previous lists. Ages are calculated on the basis of a C14 half life of 5570 yr (Godwin, 1962). Errors, including the experimental standard deviation of the counting rate of the background, of the modern standard and of the unknown sample, are expressed by 1σ (Crèvecoeur and others, 1959).

On the Relationship Between Radiocarbon Dates and True Sample Ages

The result of a radiocarbon determination is commonly expressed as an age given in radiocarbon years. An error is usually assigned to each value as a measure of the statistical uncertainty of the measurement. Date lists published in this journal use a standard form of reporting dates and their errors (see Editorial Statements in Radiocarbon, v. 3 and v. 4). The conversion of a radiocarbon age, given in radiocarbon years B.P. (i.e., radiocarbon years elapsed since the origin of the sample) to a true calendar year makes necessary certain assumptions with respect to: (1) the half-life of C14, (2) the production rate of C14 by cosmic rays, (3) the size of reservoirs into which C14 is distributed and the exchange rate of this distribution. Libby (1955, p. 10) has shown that as an approximation one may assume that reservoir size and production and distribution rates, and therefore the C14 activity in atmospheric CO2 have been constant. However, the more accurate measurements of recent years have shown that at least one of these quantities must have varied with time. This means that a more complicated relationship exists between radiocarbon age and exact calendar age of a sample than had been assumed by Libby. This relationship cannot be determined theoretically, but can be derived empirically by determination of the radiocarbon contents of samples of known age. The following summarizes our present knowledge regarding differences between radiocarbon ages and true ages and the present status of the empirical calibration of the radiocarbon time scale.

Radiocarbon Dating at the University of Washington III

This date list consists of those measurements made since 1962. The counter is one described previously (Fairhall and Schell, 1963). The results are computed using NBS oxalic acid as the standard and 5568 for the half-life of C14. Standard deviations are computed for each measurement, including the statistical error in the sample count and uncertainties in background and standard. In general, each sample is counted at least twice. The quoted error on the date is the standard deviation. A 2σ criterion is used to establish a lower limit to the age of very old samples with no detectable trace of C14. No correction for isotope fractionation has been made in any of the measurements.

Berlin Radiocarbon Measurements II

This date list covers age measurements carried out at the Radiocarbon Dating Laboratory of the German Academy of Sciences of Berlin (DAW) since 1963 and is a continuation of our first date list (Berlin I). Procedures and methods of preparing the samples are essentially the same. We completed our laboratory with a second electronic counting apparatus. Two further proportional counters with internal anticoincidence (Houtermann-Oeschger counters) are made from an old railway-car axle. The total volume of these counters is 4 L, the effective volume 2.2 L, the background 2.0 counts/min at 700 Torr (acetylene filling), and the contemporary standard value (0.95 NBS oxalic acid) is 20 counts/min. Each sample is measured twice, first for 48 hr and after 8 days for another 24 hr. Data have been calculated on the basis of a C14 half-life of 5570 yr (Godwin, 1962). Errors listed include the standard deviations (1σ) of the counting rates of the contemporary samples, the background and the unknown samples. Calculated errors less than 100 yr have been increased to that figure as a minimum.Corrections have not been made for C13 content. Mass spectrometrics C13 measurements of some samples indicate that errors resulting from fractionation are minimal.

Gif-Sur-Yvette Natural Radiocarbon Measurements I

The following list shows the age measurements carried out from 1958 to March 1963 at the Radiocarbon Laboratory at Gif-sur-Yvette, This laboratory has been replaced by a new one whose first measurements are also given in this volume.It was equipped with 2 proportional counters similar to those used in Saclay laboratory and operating with 1 atm of pure CO2. These counters were shielded by 15 cm lead, 5 cm iron and 1.5 cm of mercury.Data have been calculated on the basis of a C14 half-life of 5570 yr, in agreement with the decision of the Fifth Radiocarbon Dating Conference. As a modern carbon standard, wood taken from old furniture was used. This standard was found equivalent to 95% of the activity of the NBS oxalic acid, if a 2% Suess-effect is adopted for this wood.

Geological Survey of Canada Radiocarbon Dates IV

Most of the determinations reported here were obtained with the 2 L counter described in our first date list (GSC I). All age calculations are based on a C14 half-life of 5568 ± 30 yr and 0.95 of the activity of the NBS oxalic-acid standard, and the ages are quoted in years before 1950. The age errors include: counting errors of sample, background, and standard, the error in the half-life of C14, and an error term to account for the average variation of ±1.5% in the C14 concentration during the past 1100 yr. ‘Greater than’ ages are based on the 4 σ criterion (GSC II).

Tata Institute Radiocarbon Date List III

In this paper are reported C14 dates of archaeologic samples from the Neolithic, Harappan and Early Historic sites of India. C14 activity was counted in an Oeschger-Houtermans’ gas proportional counter. The counting gas, acetylene, was synthesized using the technique described earlier (Kusumgar and others, 1963). The dates presented here are based on 5568 yr for the half-life of C14. The conversion to A.D./B.C. scale has been made using a.d. 1950 as the reference year.