• Antwerp University Radiocarbon Dates II

      Vanhoorne, R.; Van Strydonck, M. (American Journal of Science, 1977-01-01)
    • An Improved Procedure for Wet Oxidation of the 14C NBS Oxalic Acid Standard

      Valastro, S.; Land, L. S.; Varela, A. G. (American Journal of Science, 1977-01-01)
      An improved procedure for wet combustion of 14C NBS oxalic acid standard has been devised which gives consistent high carbon yields and average delta-13C values of -19.1 per mil. The principal cause of fractionation in earlier attempts to prepare CO2 by the wet oxidation method was the inexact nature of the end-point. The new procedure employs a chocolate-brown end-point by adding 5ml more of the sulfuric acid-potassium permanganate solution after the initial reddish brown end-point is reached. The sulfuric acid-potassium permanganate solution is added to the NBS oxalic acid in a steady drop-wise flow, heat is applied to the generating apparatus, and a cycling technique is utilized to collect the CO2. Fifteen samples of the NBS oxalic acid were processed. The per cent carbon yields range from 98.8 to 100.9% with an average of 99.7% and an average delta-13C of -19.12 per mil. The results obtained by this procedure are much more consistent than previous results obtained in several laboratories by direct combustion.
    • University of Lund Radiocarbon Dates X

      Håkansson, Sören (American Journal of Science, 1977-01-01)
    • Dalhousie University Natural Radiocarbon Measurement II

      Ogden, J. Gordon; Hart, W. C. (American Journal of Science, 1977-01-01)
    • Radiocarbon, Volume 19, Number 3 (1977)

      American Journal of Science, 1977-01-01
    • US Geological Survey, Menlo Park, California, Radiocarbon Measurements I

      Robinson, Stephen W. (American Journal of Science, 1977-01-01)
    • Bratislava Radiocarbon Measurements II

      Usačev, S.; Chrapan, J.; Oravec, J.; Sitár, B. (American Journal of Science, 1977-01-01)
    • University of Miami Radiocarbon Dates X

      Piepgras, D.; Allison, M. A.; Dlugos, T.; Stipp, J. J. (American Journal of Science, 1977-01-01)
    • Quebec Radiocarbon Measurements II

      Barrette, L.; Lasalle, P.; Samson, C. (American Journal of Science, 1977-01-01)
    • Rudjer Bošković Institute Radiocarbon Measurements IV

      Srdoč, Dušan; Sliepčević, Adela; Obelić, Bogomil; Horvatinčić, Nada (American Journal of Science, 1977-01-01)
    • Harwell Radiocarbon Measurements II

      Otlet, R. L. (American Journal of Science, 1977-01-01)
    • Notice to Readers

      American Journal of Science, 1977-01-01
    • Index

      American Journal of Science, 1977-01-01
    • Discussion: Reporting of 14C Data

      Stuiver, Minze; Polach, Henry A. (American Journal of Science, 1977-01-01)
    • Laboratories

      American Journal of Science, 1977-01-01
    • Mineralogical Studies on Bone Apatite and Their Implications for Radiocarbon Dating

      Hassan, Afifa A.; Termine, John D.; Haynes, C. Vance (American Journal of Science, 1977-01-01)
      Infrared (IR) spectrophotometry and X-ray diffraction (XRD) were conducted on modern and fossil bone material from archaeological sites in the U S to determine post-mortem changes in bone apatite and to evaluate the effect of these changes on radiocarbon dating. IR absorption bands, XRD peak-broadening parameters, and XRD unit cell measurements indicated that during fossilization, bone apatite, a mineral similar to dahllite, was partially or completely recrystallized to francolite. Post-mortem changes involved then removal of some of the endogenous crystal carbonate both at surfaces and at internal OH-sites and introduction of exogenous carbonate into internal crystal P04 sites. Increased fluorine content accompanied carbonate substitution. Both the carbon isotopic composition and the amount of exogenous carbonate introduced into the apatite structure will affect the radiocarbon dating of bone apatite. Special sample pre-treatment may remove most of the substituted carbonate in some cases. Simulated experiments are suggested for a better understanding of the nature and mechanism of carbonate substitution in bone apatite for the removal of the exogenously substituted carbon and the improvement of radiocarbon dates.