Correction For Isotopic Fractionation Research Articles

ERRATUM: Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

The error appeared in calculations of the sulfur isotopic fractionation correction.

A critical review on isotopic fractionation correction methods for accurate isotope amount ratio measurements by MC-ICP-MS

Proper correction of mass-dependent and mass-independent isotopic fractionation is crucial to obtain accurate isotope amount ratios by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS).

87Sr/86Sr isotope ratio measurements by laser ablation multicollector inductively coupled plasma mass spectrometry: Reconsidering matrix interferences in bioapatites and biogenic carbonates

This study is dedicated to the systematic investigation of the effect of interferences on Sr isotopic analyses in biological apatite and carbonate matrices using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC ICP-MS). Trends towards higher 87Sr/86Sr ratios for LA-MC ICP-MS compared to solution-nebulization based MC ICP-MS when analysing bioapatite matrices (e.g. human teeth) and lower ratios in case of calcium carbonates (e.g. fish ear stones) were observed. This effect can be related to the presence of significant matrix-related interferences such as molecular ions (e.g. (40Ca-31P-16O)+, (40Ar-31P-16O)+, (42Ca-44Ca)+, (46Ca40Ar)+) as well as in many cases concomitant atomic ions (e.g. 87Rb+, 174Hf2+). Direct 87Sr/86Sr ratio measurements in Ca-rich samples are conducted without the possibility of prior sample separation, which can be accomplished routinely for solution-based analysis. The presence of Ca-Ar and Ca-Ca molecular ion interferences in the mass range of Sr isotopes is shown using the mass resolving capabilities of a single collector inductively coupled plasma sector field mass spectrometer operated in medium mass resolution when analysing bioapatites and calcium carbonate samples.The major focus was set on analysing human tooth samples, fish hard parts and geological carbonates. Potential sources of interferences were identified and corrected for. The combined corrections of interferences and adequate instrumental isotopic fractionation correction procedures lead to accurate data even though increased uncertainties have to be taken into account. The results are discussed along with approaches presented in literature for data correction in laser ablation analysis.

Relationship between stable carbon and nitrogen isotope ratios of humic acids extracted from Andisols and non-Andisols

To relate the isotopic composition of soil humic acids (HAs) to their source plants and their degree of humification (as indicated by the degree of darkening), as well as to soil type, we determined the stable isotope ratios for carbon (δ13C) and nitrogen (δ15N) of HAs extracted from 26 virgin soil samples (14 Andisols and 12 non-Andisols) and from leaf samples from ten C3 plants and seven C4 plants. The high absorption coefficients (estimated at 600nm for 1% solutions), low hydrogen and nitrogen contents, low H/C ratios, low alkyl C and O-alkyl C contents, high O/H and C/N ratios, high aryl C contents, and high aromaticity of the Andisol HAs indicated a high degree of humification. The δ13C and δ15N values of the non-Andisol HAs increased along with the progression of humification of C3 plant-derived HAs. A significant correlation was observed between the δ15N and δ13C values of the non-Andisol HAs, but not for the Andisol HAs. Most of the Andisol HA δ13C values were higher than the highest non-Andisol HA δ13C value, and δ13C values were distributed between the δ13C values for the C3 and C4 plants. The contributions of C4 plant-derived carbon to total Andisol HA carbon (CRC4) are usually calculated on the assumption that the δ13C values are not substantially altered during the decomposition of plant materials and the formation of soil organic matter. However, if 13C enrichment occurs during organic matter decomposition, CRC4 will be overestimated. Therefore, we suggest a new method to calculate CRC4 values of Andisol HAs with a correction for isotopic fractionation associated with microbial degradation; the corrected CRC4 values ranged from −5% to 58% and were approximately 22% lower than the uncorrected values.

Doubly Labeled Water Is a Validated and Verified Reference Standard in Nutrition Research

The doubly labeled water (DLW) method is currently the most relevant, albeit expensive, method for measuring free-living energy expenditure in animals and humans. The DLW method is based on the exponential disappearance from the body of the stable isotopes 2H and 18O after a bolus dose of water labeled with both isotopes. The 2H is lost as water and the 18O as both water and CO2. After correction for isotopic fractionation, the excess disappearance rate of 18O relative to 2H is a measure of the CO2 production rate (1). This rate can be converted to an estimate of total energy expenditure by using a known or estimated respiratory quotient and the classical principle of indirect calorimetry (2). The DLW technique, however, is not without limitations because it uses several assumptions such as a constant rate of CO2 production and constant size of body water pool throughout the measurement period. In addition, not all researchers use the same methods to calculate the isotope pool spaces, the constant elimination rate, the fractionation factors, and the mode of CO2 conversion to energy expenditure. The DLW method was first proposed by Lifson et al. (3) in the middle of the last century, but its application to human studies was delayed for some 30 y (4) until improvements in analytical instrumentation made such investigations feasible. Since this pioneering work, the use of DLW has progressed, first to a research tool for the measurement of energy metabolism in free-living humans and later to the status of the “gold standard” to which most newly developed methodologies are compared. Unlike some other methods, DLW has matured relatively slowly and has been subject to frequent retrospective reviews by expert practitioners, which has led to substantial international agreement on matters of principle and practice (5). The benefit of such an approach is that it ensures compatibility between results from different laboratories so that direct comparisons can be made. Furthermore, it provides new investigators with a rigorous framework for experimental design and interpretations, thus ensuring that the results reported are of the highest quality (5). The next significant step in establishing DLW as a reference standard in energy metabolism research is work presented in the current issue of The Journal of Nutrition by Wong et al. (6). As the authors pointed out, the long-term reproducibility of the DLW method has not been reported. Providing this clearly missing evidence could be especially important for longitudinal monitoring of changes in energy expenditure, energy intake, and body composition in human and perhaps in animal research. The experimental protocol of the study was based on the multicenter, parallel-group, randomized controlled clinical trial Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy (CALERIE), described in detail previously (7). The parent study created an ideal nest for evaluating the longitudinal reproducibility of the DLW method. The present study included 2 protocols, 1 for the study dose dilutions and 1 for test-retest reliability. The experimental procedure, which can be highly error prone (8), was conducted with a high degree of technical precision and in a double-masked fashion by using isotope ratio mass spectrometer methodology. The first protocol showed that the theoretical fractional turnover rates for 2H and 18O and the difference between the 2 fractional turnover rates were reproducible to within 1% and 5%, respectively, over 4.4 y. The second protocol showed high reproducibility of primary DLW outcome variables such as the fractional turnover rates and isotope dilution spaces for 2H and 18O and total energy expenditure over 2.4 y. Thus, the study provided a unique set of scientific data and clearly demonstrated the feasibility of the DLW method in longitudinal studies to examine energy balance changes in humans. Although the study was conducted in adults, there is no compelling reason to believe that the results would be different in other populations, such as children and older adults. The detailed protocols presented by Wong et al. (6) could be used by other researchers in their laboratories to document the long-term reproducibility of their measurements to ensure the biologic significance of the long-term outcomes of interest. The data set could also be used to validate recently introduced new and less costly alternative methods for the high-precision water isotope abundance analyses (9, 10). One of the unresolved issues in nutritional research over the past 100 y has been unobtrusive measurement of dynamic changes in total energy balance with high accuracy and precision and for periods longer than a few days or months. These measures are important because total energy is the only nutrient for which intake is regulated physiologically independent of weight and physical activity. It has been documented that small, albeit long-term, changes in the total energy balance could affect body weight or composition with a potential for well-known health effects such as obesity. Previous studies used labeling of total body water and measuring outflow rates to monitor changes in energy intake and expenditure and to provide estimates of energy balance–related changes in body composition (1). By using the data from the CALERIE study (7), Wong et al. (6) provided compelling evidence that the DLW method could be used in clinical trials to monitor adherence to dietary protocol, changes in energy intake, and changes in body composition. Although methodologic uncertainties are likely to persist in the near future primarily because of the described and other limitations of the DLW method, the study by Wong et al. provides us with tools to decrease these limitations. In conclusion, the results of Wong et al. (6) and other recent advances in stable isotopes of water analysis (9, 10) solidify the validity of DLW as the reference standard for measurement of energy expenditure in the free-living and the applicability of DLW-derived applications in nutrition research.

Determination of the Biobased Content in Plastics by Radiocarbon

Accelerator mass spectrometry (AMS) radiocarbon analyses were performed on biobased unsaturated polyester resins in order to assess the potential of the method for the determination of the bio-fraction. Different resins were synthesized in the laboratory with different proportions of raw materials of biogenic origin, and analyzed both in the liquid and in the solid form. As a preliminary step of the study, both the biobased and the fossil-derived raw materials were analyzed in order to determine their 14C content. A comparison of the obtained results with the expected ones allowed us to investigate the potential of the 14C method in this field as well as to address some still open issues such as the levels of uncertainty and accuracy as related to the calculation procedures, the correction for isotopic fractionation, and the effect of the presence of volatile components in the analyzed materials.

Quantum-mechanical equilibrium isotopic fractionation correction to radiocarbon dating: a theory study.

This paper relates the quantum–mechanical equilibrium isotopic fractionation correction to the radiocarbon dating method by Eq. 9, and also shows the significant influence of temperature on the method. It is suggested that the correction is a function of the frequencies and temperature of a specific sample and these two variables can be evaluated theoretically by the ab initio quantum calculations and experimentally by analyzing the clumped-isotope ratios in it, respectively. This paper also suggests that the 14C/12C ratio in the atmosphere in geological time can be calculated by Eq. 10.

Low-energy 14C AMS in Poznań Radiocarbon Laboratory, Poland

Poznań Radiocarbon Laboratory is equipped with the “Compact Carbon AMS” machine produced by NEC, and the self-designed lines for graphite production from natural samples. Our AMS machine is characteristic first by a low voltage accelerator, that makes the spectrometer construction simpler, its size smaller and the maintenance easier than in case of the larger AMS 14C systems.Despite simpler construction of the AMS spectrometer, the quality of our 14C results is comparable to those obtained with larger AMS systems. A few months activity of the laboratory demonstrated high precision of the AMS machine and fine purity and good reproducibility of graphite target preparation. Though our AMS machine background is rather high (≈0.1 pMC), it is still a minor part of our 14C blank (0.25–0.3 pMC), which is comparable to that found in many AMS 14C facilities. Our standard precision of single cathode 14C/12C measurement of a modern sample corresponds to 0.3 per mil. This, together with simultaneous measurements of 13C/12C ratio (and correction for isotopic fractionation), enables single cathode 14C dating of young samples with an error of ±30 years. Accuracy of dating is not significantly worse, which has been demonstrated by the tests with samples of known age.

Low-energy 14C AMS in Pozna Radiocarbon Laboratory, Poland

Poznań Radiocarbon Laboratory is equipped with the “Compact Carbon AMS” machine produced by NEC, and the self-designed lines for graphite production from natural samples. Our AMS machine is characteristic first by a low voltage accelerator, that makes the spectrometer construction simpler, its size smaller and the maintenance easier than in case of the larger AMS 14C systems. Despite simpler construction of the AMS spectrometer, the quality of our 14C results is comparable to those obtained with larger AMS systems. A few months activity of the laboratory demonstrated high precision of the AMS machine and fine purity and good reproducibility of graphite target preparation. Though our AMS machine background is rather high (≈0.1 pMC), it is still a minor part of our 14C blank (0.25–0.3 pMC), which is comparable to that found in many AMS 14C facilities. Our standard precision of single cathode 14C/12C measurement of a modern sample corresponds to 0.3 per mil. This, together with simultaneous measurements of 13C/12C ratio (and correction for isotopic fractionation), enables single cathode 14C dating of young samples with an error of ±30 years. Accuracy of dating is not significantly worse, which has been demonstrated by the tests with samples of known age.

Validation of the doubly‐labeled water (DLW) method for estimating CO2 production and water flux in growing poultry chicks

This study is the first validation of the doubly‐labeled water (DLW) method on birds (1) to evaluate the accuracy of 2 points versus multiple points for computing fractional isotopic washout rates (k) and CO2 production (rCO2), (2) to measure CO2 production and water flux each day over a 4‐day period, (3) to compare measured fractional evaporative water loss (rG) with assumed values that provide DLW estimates of rCO2 with zero error, and (4) to measure the effect of assumed rG on the error of estimating water influx and efflux. Percent error of CO2 production of six growing poultry chicks estimated by the DLW method was not correlated with mean daily relative growth rates of up to 5% nor with daily rates of energy retained in growth of up to 320 kJ/day/kg, nor was it significantly reduced by using multiple points (5 points) rather than 2 points to compute fractional isotopic washout rates (k) and isotope pool sizes. Its seems clear from our study and the previous 5 validations on growing birds that average relative daily growth rates of up to about 20% do not increase the error of estimating rCO2 by the DLW method. Arithmetic error was significantly less when using one isotopic pool, rather than two pools, to compute rCO2 and was less when using an assumed fractional evaporative water loss (rG) of 0.45 rather than an assumed rG of 0.25 or 0.5 (the two values used predominantly in previous DLW studies). Our study supports Speakman's (1997) suggestion that the one‐pool model is more appropriate than the two‐pool model for birds weighing<1 kg. We recommend using an assumed rG of 0.45 to compute rCO2 of poultry, which is a compromise between the two schools of rG useage, i.e., rG=0.25 or 0.5, however we hesitate to recommend 0.45 for all birds in all settings. Close agreement between measured rG and an assumed rG that produced zero rCO2 error supports the validity of using the pooled fractionation correction factors (fpool) of 0.0339 for tritiated water and 0.0249 for deuterated water. Absolute error decreased with the percent washout of during measurement periods of 1 to 4 days. Accuracy of estimating rCO2 was not significantly different for durations of 2, 3, and 4 days using either tritiated or deuterated water. The arithmetic error of estimating rCO2 using a one isotopic pool model, 2 points, an rG of 0.5, and tritiated water was −1.9% (SD=13.5) for the first day of a 4‐day period and −4.0% (SD=8.9) for the entire period. Percent arithmetic error of water influx (rH2Oinf) and efflux (rH2Oeff) estimated for day 1 from tritiated water washout and an assumed rG of 0.5 was −0.5 (SD=6.4) and 0.1% (SD=11.1), respectively. An rG of 0.5 produced significantly less arithmetic error than an rG of 0.25 or an rG of zero (i.e., no fractionation correction), and less absolute error in rH2Oinf. Errors were slightly more negative (underestimates) with an rG of 0.25, i.e., −2.2 and −2.0%, respectively and even more negative with no correction for isotopic fractionation (i.e., an assumed rG of zero). Tritiated water estimates of water influx and efflux during the first day had no error when using an rG of 0.57 and 0.48, respectively. With assumed rGs of 0.25 and 0.5, the errors of water influx were −7.8 and −5.9%, and the errors of water efflux were 3.4 and 5.6%, respectively, over 4 days. We recommend using an assumed rG of 0.45 to compute rH2Oeff for poultry. The error of rCO2 was about 3 to 4 times more sensitive to values of assumed rG than the error of water flux.

Use and analysis by thermal ionisation mass spectrometry of 26Mg and 41K to assess mineral uptake in Scots pine (Pinus sylvestris L.)

Use of 26Mg and 41K as tracers allows the quantification of the uptake and internal cycling of Mg and K in plants. Application of thermal ionisation mass spectrometry (TIMS) used for a plant experiment is discussed here. Firstly, the sensitivity of the 26Mg/24Mg ratio to the amount of Mg loaded onto the mass spectrometer filament was assessed. Using NIST SRM-980 and amounts of Mg from 0.2 to 1.2 μg, no significant difference in the 26Mg/24Mg value after correction for isotope fractionation was observed. Analysis of SRM-980 produced a corrected mean 26Mg/24Mg value of 0.13960 ± 0.00006 (n = 10) close to the certified range (0.13932 ± 0.00026). Control of fractionation during K analysis by TIMS is important for accurate isotope determinations. Fractionation profiles for NIST SRM-985 using filament loadings of 1 and 5 μg K were plotted and, with the higher loading, produced a more stable 39K/41K value. Conversion of K from a chloride to an iodide had no significant effect on the measured ratio. The SRM-985 mean 39K/41K value was 13.916 ± 0.034, higher than the certified range (13.8566 ± 0.0063). Analysis of natural 26Mg and 41K levels in needles, stem wood, stem bark, fine roots and coarse roots from Scots pine allowed the precision of the analysis to be defined. This information, in conjunction with a simple model, was used to discuss the design of a tracer study in plants using 26Mg and 41K. Predicted whole tree 39K/41K and 26Mg/24Mg values from a 95 day experiment were then calculated and compared with the actual values measured using TIMS.

Isotopic ((13)C) fractionation during plant residue decomposition and its implications for soil organic matter studies.

Carbon isotopic fractionations in plant materials and those occurring during decomposition have direct implications in studies of short-and longer-term soil organic matter dynamics. Thus the products of decomposition, the evolved CO(2) and the newly formed soil organic matter, may vary in their (13)C signature from that of the original plant material. To evaluate the importance of such fractionation processes, the variations in (13)C signatures between and within plant parts of a tropical grass (Brachiaria humidicola) and tropical legume (Desmodium ovalifolium) were measured and the changes in (13)C content (signatures) during decomposition were monitored over a period of four months. As expected the grass materials were less depleted in (13)C (-11.4 to -11.9 per thousand) than those of the legume (-27.3 to -25.8 per thousand). Root materials of the legume were less (1.5 per thousand) depleted in (13)C compared with the leaves. Plant lignin-C was strongly depleted in (13)C compared with the bulk material by up to 2.5 per thousand in the legume and up to 4.7 per thousand in the grass. Plant materials were subsequently incubated in a sand/nutrient-solution/microbial inoculum mixture. The respiration product CO(2) was trapped in NaOH and precipitated as CaCO(3), suitable for analysis using an automated C/N analyser coupled to an isotope ratio mass spectrometer. Significant depletion in (13)C of the evolved CO(2) was observed during the initial stages of decomposition probably as a result of microbial fractionation as it was not associated with the (13)C signatures of the measured more decomposable fractions (non-acid detergent fibre and cellulose). While the cumulative CO(2)-(13)C signatures of legume materials became slightly enriched with ongoing decomposition, the CO(2)-C of the grass materials remained depleted in (13)C. Associated isotopic fractionation correction factors for source identification of CO(2-)C varied with time and suggested errors of 2-19% in the estimation of the plant-derived C at 119 days of incubation in a soil of an intermediate (-20.0 per thousand) (13)C signature. Analysis of the residual material after 119 days of incubation showed little or no change in the (13)C signature partly due to the incomplete decomposition at the time of harvesting. Copyright 1999 John Wiley & Sons, Ltd.

Biological nitrogen fixation estimated by [formula omitted] dilution, natural [formula omitted] abundance, and N difference techniques in a subterranean clover–grass sward under Mediterranean conditions

Pasture legumes are used as a source of biologically fixed N 2. Several methods have been used to evaluate the amount of N 2 fixed in mixed pastures, but none is considered clearly superior. In a Eutric Leptosol of southern Portugal, N 2 fixation by subterranean clover mixed with grasses was evaluated over 2 years and subjected to several cuts by 15 N dilution (ID), natural 15 N abundance (NA) and N difference (ND) techniques. The amount of fixed N 2 in subterranean clover determined by natural 15 N abundance with correction for isotopic fractionation ranged from 32 kg N ha −1 in 1992/1993 to 37 kg N ha −1 in 1993/1994. Assuming that no isotopic fractionation occurred during fixation ( B=0‰), fixation capacities at around 80% of nitrogen derived from the atmosphere (Ndfa) were found by the natural 15 N abundance technique. However, with correction for isotopic fractionation during N 2 fixation ( B=−1.13‰), fixation capacities closer to 50% Ndfa were obtained, similar to the value obtained in the second-year experiment with the isotopic dilution method. In year 1, the fixation capacity, as estimated by the isotopic dilution method, was about 37% Ndfa. The nitrogen difference (clover N−grass N) calculations underestimated the amount of N 2 fixed in 1992/1993. This method assumes that both legumes and non-legumes absorb the same amount of N from the soil, which may not be true. Also, only the above-ground legume herbage was analyzed in this experiment. From the results, either ID or NA methods, particularly with a correction for the B-value, can be used to estimate N 2 fixation in mixed pastures, rather than the ND method. The natural 15 N abundance (NA) technique can be more versatile than the ID technique, allowing frequent sampling in undisturbed grassland ecosystems with reduced costs. Nitrogen fixation decreased in June, in both years, probably due to a lower soil water content and higher soil temperature.

Radiocarbon Dating of Ostrich Eggshells

Unlike wood charcoal, as found admixed to other cultural remains, ostrich eggshells can be of more direct significance in 14C dating, especially if they were processed to form, eg, eggshell beads. Normally the time span between laying the egg and working the shell beads is short enough to be negligible for 14C dating purposes. Another advantage of eggshell dating is that the carbonate of the shell seems to keep exceptionally well over the millennia, whereas, especially in surface sites in a desert environment, organic material such as wood, charcoal or bone protein tends to decompose. With few comparative test samples, we thought ostrich egg samples would yield 14C dates somewhat too young. The deviation is, however, balanced by performing 13C analyses and a correction for isotope fractionation of ca 350yr.

Radiocarbon determination of atmospheric methane at Baring Head, New Zealand

Although methane in the atmosphere is clearly increasing, its sources are still poorly defined. Measurement of carbon isotope ratios allows constraints to be placed on relative source strengths of atmospheric methane because different potential sources have different isotope ratios. Unfortunately, interpreting 13C/12C ratios of atmospheric methane is subject to uncertainty because a correction for isotope fractionation in the oxidation of methane is not well determined. Interpreting 14C/12C ratios is also complicated by the need to correct for release of 14CH4 from nuclear power plants using rough estimates. Simultaneous use of both carbon isotope ratios, however, improves the confidence of interpretation. Here we show that measurements of the 14C/12C ratio, using accelerator mass spectrometry, and 13C/12C ratio of methane from clean Southern Hemisphere air are consistent with current estimates of both types of correction and imply that about 32% of atmospheric methane is derived from fossil carbon sources.

In vivo isotope-fractionation factors and the measurement of deuterium- and oxygen-18-dilution spaces from plasma, urine, saliva, respiratory water vapor, and carbon dioxide

In vivo isotope-fractionation factors were determined for hydrogen and oxygen between plasma water samples and samples of urine, saliva, respiratory water vapor, and carbon dioxide in 20 normal adults. The isotope-fractionation factors ranged from 0.944 to 1.039 for 2H in breath water vapor and for 18O in breath CO2, respectively. When corrected for isotope fractionation, the 2H- and 18O-dilution spaces determined from urine, saliva, respiratory water, and CO2 were within -0.10 +/- 1.09 kg (mean +/- SD, n = 60) and 0.04 +/- 0.68 kg (n = 80), respectively, of the values determined from plasma. In the absence of these corrections, we observed a 6% overestimation of 2H-dilution space and a 1% overestimation of 18O-dilution space from the use of respiratory water values. A 4% underestimation of the 18O-dilution space was observed for breath CO2 without correction for isotope fractionation.

Carbon Isotope Analysis of Land Snail Shells: Implications for Carbon Sources and Radiocarbon Dating

13C and 14C analyses were performed on a series of modern Jamaican land snails in order to quantitatively determine the sources of shell carbon. A model of these carbon sources, the pathways by which carbon reaches the shell, and the fractionation processes involved are presented. The contribution of limestone to shell carbonate is variable but may comprise up to 33% of the shell. About 25–40% of shell carbonate is derived from plants and about 30–60% from atmospheric CO2. Variation among populations and species with respect to 13C and 14C is attributed to the effects of limestone incorporation, snail size (as it affects CO2 exchange rate), physiological characteristics (presence of urease, respiration rate), and activity patterns of the snails. A formula for correction for isotopic fractionation of 14C of shell carbonate, based on 13C measurements, is derived. Bicarbonate-aragonite fractionation is apparently very minimal. Shell organic carbon appears to be derived largely from plants but also to a lesser extent from inorganic hemolymph carbon. This introduces the possibility of a small age anomaly of shell organic 14C due to limestone incorporation.

Isotopic Fractionation of NBS Oxalic 14C Standard and Its Effect On Calculated Age of Materials

There is much controversy about the significance to radiocarbon dating of isotopic fractionation during the oxidation to CO2 of NBS oxalic acid, the carbon-14 dating standard. To check the effect of fractionation, 30 routine potassium permanganate oxidations of oxalic acid were performed. The isotopic composition of resulting CO2 was determined mass-spectrometrically. δ13C results ranged between —17.7 and —21.2, with an average of —18.9‰ wrt PDB. The effect of not applying an isotopic fractionation correction to NBS oxalic acid when performing age calculations is evaluated.

University of Washington Geosecs North Atlantic carbon-14 results

The 14C activities of North Atlantic water at Geosecs stations 5, 27, and 29 are reported. The influence of the correction for isotope fractionation on the 14C results is discussed, and experimental procedures are given.

Riken Natural Radiocarbon Measurements I

Natural C14 measurements at the Institute of Physical and Chemical Research (RIKEN) became routine in 1962. The counters presently used are made of stainless steel with a volume of about 2.7 L. They are surrounded by 2.5 cm of pure lead, a ring of 22 propane gas-flow anticoincidence counters, about 10 cm of boric acid and 20 cm of iron. When filled with dead CO2 up to 2 atm, they gave a background counting rate of about 9 cpm (Hamada, 1960).In this article, results obtained for geologic and archaeologic samples since 1962 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. Correction for isotopic fractionation was not applied.