• High-Precision 14C Measurement of Irish Oaks to Show the Natural 14C Variations from 200 BC to 4000 BC

      Pearson, G. W.; Pilcher, J. R.; Baillie, M. L. (American Journal of Science, 1983-01-01)
      Bi-decade samples of dendrochronologically matched Irish Oak, measured with a precision of ca +/20 years, covering the period 200 to 4000 BC are presented. The data are compared with the published data of Suess, de Jong, and Mook to provide a general calibration of the 14C time scale for this period. Although the dendrochronologic sequences presented are not absolutely tied to present, the best fit (based on 14C evidence) of the Belfast data to absolute chronologies, the error and evidence associated with such positioning is given. The intervals chosen for analysis were 20 years, reducing slightly the resolution of short-term variations when compared to 10-year intervals, which are sometimes measured. However, this calibration would suffice for most scientific purposes and certainly for the calendrical conversion of 14C dates derived from archaeologic samples.
    • High-Precision 14C Measurement of Irish Oaks to Show the Natural Atmospheric 14C Variations of the AD Time Period

      Pearson, G. W.; Baillie, M. G. L. (American Journal of Science, 1983-01-01)
      The high-precision 14C measurement of bi-decade and decade samples of Irish Oak for the time period AD 50 to 1830 is presented. The samples were taken from dendrochronologically dated Irish Oak providing an absolute chronology for this period. While the natural atmospheric 14C concentration shows cyclic deviations from a constant value, the amplitudes of such deviations vary considerably. Repeated measurement and interlaboratory checks justify a claim to accuracy in the data given. Comparison of a large number of data sets between Belfast and Seattle show that the different techniques of scintillation counting of 14C6H6 and gas counting of 14CO2 derived from different wood species grown in different continents give no significant bias. Thus, it is justifiable to use this data set as a high-precision calibration curve for the AD period. Over most of this period bi-decade samples were measured giving a slightly reduced resolution of shortterm variation when compared to the measurement of decade intervals; however, any difference is not apparent when such curves are compared. It is of much greater importance that a comparison of data sets is without bias if a combined calibration curve is to have sufficient integrity for general use. Averaging the data from Belfast and Seattle would improve the validity of such an AD 14C calibration curve since it would tend to smooth out slight local variations and become internationally more acceptable.
    • Possible Depletion in 14C in Trees Growing in Calcareous Soils

      Tauber, Henrik (American Journal of Science, 1983-01-01)
      14C activities of decadal samples from beech trees growing under extreme calcareous conditions were compared to 14C activities of decadal samples of the same age from a beech tree growing in a normal mold soil in order to see whether part of the carbon assimilated during photosynthesis might originate from 14C-deficient carbonates in the soil. The calcareous soils contained from 18 to 52% calcium carbonate, and this carbonate had a mean 14C age of 10,200 to 17,600 years BP. A comparison was also made with the 14C activity of contemporaneous samples from Douglas Fir from the US North Pacific (Stuiver, 1982). No significant depletion in 14C activity in beech trees growing in the highly calcareous soils was detected. The measured mean difference in 14C activity in beech trees from calcareous and non-calcareous sites corresponds to an uptake of 0.12 +/- 0.3% carbon from soil carbonates in the calcareous sites.
    • Radiocarbon Dating in the Arctic Region

      Olsson, Ingrid U. (American Journal of Science, 1983-01-01)
    • The Radon Problem in 14C Dating

      Nydal, Reidar (American Journal of Science, 1983-01-01)
      Due to traces of radium and uranium in most 14C samples, radon appears as a radioactive contamination in the CO2 prepared by combustion. This contamination must be removed by an active purification prodecure or by storing the CO2 prior to measurement. No effective electronic discrimination against radon and its daughter elements can be performed. The necessary storage time until radon has decayed varies widely, especially for marine shells. The latter material, collected from Norway and Svalbard, has been a main object for the present investigation. In a few cases, a measureable amount of radon may be left even after eight weeks. The behavior of radon and its daughter elements in a CO2 proportional counter has been studied.
    • The Unreliability of 14C Dates Obtained from Buried Sandy Podzols

      Geyh, Mebus A.; Roeschmann, Günter; Wijmstra, T. A.; Middeldorp, A. A. (American Journal of Science, 1983-01-01)
      A test for the reliability of 14C dating of soil was made at two sites with buried, autochthonous, and in parts, allochthonous sandy podzols, dated either lithoand pedostratigraphically or palynologically. The differences between the age ranges obtained and the apparent mean residence times (AMRT) calculated from the 14C content of alkaline extracts from fossil soil layers and horizons lean in organic matter exceed 10,000 years, corresponding to a maximum contamination with recent carbon of up to 50 %. The use of correction factors for the apparent mean residence times of podzols is not valid, not even for climate zones, because these values have a broad scatter for the same profile.