Carbon-14 dates at grande pile: correlation of land and sea chronologies

Sixteen radiocarbon dates extending back to 70,000 years provide a chronology for the continuous continental pollen record of Grande Pile. This record reflects climatic changes over the last 140,000 years in northeastern France. The cold period initiating the Middle Weichselian, dated previously at 55,000 years, is dated at 70,000 years before the present (B.P.) at Grande Pile. This event is marked by the disappearance of deciduous forests at this site. The Early Weichselian is placed before 70,000 years B.P. A correlation with the oxygen isotope stages from oceanic records is demonstrated until 70,000 years B.P. and attempted beyond.     

Carbon-14 dating: a comparison of Beta and ion counting

Accelerator ion counting compares favorably with conventional beta counting. The major advantage of ion counting is that milligram samples can be analyzed. When sample size is not limiting, ion counting complements beta counting for the more routine carbon-14 determinations. Further development is needed before ion counting can achieve the same high precision as beta counting for large samples (+/- 2 per mil). A solution to the background variability has to be found before ion counting can be used to date samples back to the 75,000-year limit of beta counting.     

Carbon-14: direct detection at natural concentrations

The (14)C atoms naturally present in a piece of 19th-century wood have been detected directly by means of a tandem Van de Graaff accelerator used as a high-energy mass spectrometer. The (14)C ions were easily resolved from interfering ions with the use of a DeltaE-E detector telescope (this telescope consists of a pair of detectors; one of them measures the specific ionization, DeltaE, and the sum of the signals from both detectors gives the total energy for each ion, ET). The technique offers a number of practical advantages.     

Carbon-14 in patagonian tree rings

The radiocarbon activity found in tree rings from southern Argentina shows secular fluctuations which are synchronous with and of the same amplitude as those known for the Northern Hemisphere. Comparable measurements indicate that the activity in Patagonian trees is about five per mil lower than in European trees.     

Carbon-14 trends in subfossil pine stubs

Subfossil pine stubs from a peat bog in the Netherlands were linked together dendrochronologically and sampled at intervals of 30 or 50 years for carbon-14 analysis. The results suggest that the carbon-14 content of the atmosphere was not changing between about 5400 and 5100 B.C., but that it was increasing slightly about 800 years earlier.     

Carbon-14 dating of small samples by proportional counting

Conventional carbon-14 dating by means of gas proportional counters has been extended to samples containing as little as 10 milligrams of carbon. The accuracy of the dating procedure has been checked by dating sequoia tree-ring samples of the 1st century A.D. and B.C. and an oak tree-ring sample of the 19th century A.D.     

Carbon-14 and tritium measurement by means of bremsstrahlung emissions

The feasibility of measuring carbon-14 and tritium in vivo has been demonstrated in the rat; thin scintillation detectors were used for the measurement of bremsstrahlung produced by these soft beta emitters. Measurements of tritium in vivo are limited to the study of surface phenomena, whereas bremsstrahlung produced by carbon-14 may be detected from depths of several centimeters.     

Carbon-14 milk constituents from cows fed carbamate labeled with carbon-14 on the carbonyl

Oral administration to a dairy cow of Furadan insecticide (2,2-dimethyl-2,3-dihydro-7-benzofuranyl N-methylcarbamate) labeled with carbon-14 on the carbonyl produced in the milk certain radioactive materials which were not Furadan metabolites. The data suggest that these products were natural milk constituents containing only the carbon-14 atom from the Furadan molecule. Carbon-14-labeled carbon dioxide formed by the hydrolysis of the carbamate insecticide is the apparent precursor of these radiolabeled constituents of the milk.     

Carbon-14 Dating with the Liquid Scintillation Counter: Total Synthesis of the Benzene Solvent

Samples are analyzed for natural radiocarbon content by a total synthesis of benzene from their organic constituents. The benzene is employed as the solvent in a liquid scintillation counter. The instrument used permits 15grams of carbon to be counted with an efficiency of 40 percent and a background of 13 counts per minute.     

Carbon-14 in methane sources and in atmospheric methane: the contribution from fossil carbon

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric (14)GH(4) seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 +/- 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 +/- 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH(4) concentrations, and delta(13)C in CH(4) indicate that 21 +/- 3% of atmospheric CH(4) was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of (14)CH(4).