Since 1994, a new data-acquisition system with rise-time (RT) based background reduction has been in operation at the Gliwice Radiocarbon Laboratory. During long-term stability tests, we observed large shifts in the RT spectra obtained during various measurement series. These shifts caused important changes in the count rate measured with RT reduction. As a result, we have ascertained that the shifts are the consequence of variable concentration of electronegative impurities. A correction method was considered, using average RT of pulses obtained in coincidence with the muon events, so-called ARTL (average rise time of L pulses), for estimation of the RT of the spectrum's shift. However, radiocarbon dates calculated based on count rates with RT discrimination, which were corrected using this method, are not more precise than traditional 14C dates. Nevertheless, the value of the average coincidence pulse RT is a good indication of sample gas purity.

A significant reduction in cosmic-ray activity and backgrounds of the gas-filled proportional counters, as measured in a heavy iron shield, was observed when the Uppsala Conventional 14C Laboratory was moved in 1984. The new site was better shielded from cosmic rays because of additional concrete layers above the laboratory. A study that lasted over one year yielded a figure for the muon reduction. The backgrounds were reduced approximately to the extent expected from the soft-component contribution at the old Laboratory as judged from barometric-pressure dependence. After a few years, new electronics enforced, and enabled, the revision and improvement of the standard values for the activity and age calculations.

A careful analysis of the results for the counters has increased the accuracy of the small corrections needed to yield internal error-multiplication factors mostly between 1 and 1.5 for the background for short periods of up to 12 months, and <1.1 for the oxalic acid samples combined for the last few years of measurements in the laboratory. Similar results were obtained for two counters.

β-counting software programs were developed and installed in new PCs for operation under a Windows® NT workstation. The new software programs allow us to simultaneously control several β-counting systems, either remotely or from within the laboratory. This setup is much less expensive than our previous arrangement, which required a separate PC for each counter.

A recent broad study of the background of all types of low-level beta and gamma detectors has now made it possible to analyze its components more reliably and with greater detail. This general analysis is developed further here for gas proportional and liquid scintillation counters used in radiocarbon dating. The background of gas counters, which is dominated by secondary cosmic gamma radiation, is now well understood and can be described quantitatively. The background of liquid counters is less well understood and can only be described semiquantitatively, its analysis resting partly on estimates. Methods to reduce the background of both types of systems are described and their effectiveness discussed. This analysis may help in evaluating the quality of existing systems as well as in designing better ones.

This study compares vanadium oxide catalysts from three different sources: Noakes (N), Harshaw Chemical (H) and Kh. Arslanov at the St. Petersburg State University, Russia (R). The catalysts are used to convert acetylene to benzene in the last step of benzene synthesis. The organic purity of benzene in all three catalysts is high; 99.91–99.93% for (N) and (H) and 99.87% for (R). The benzene yields range from 90.0 to 94.3%. (N) averaged 92.6%, (H) averaged 91.1% and (R) averaged 92.0%. A conversion residue in the catalysts was analyzed for δ13C and found to be isotopically lighter relative to acetylene by −2.2% for (N) and (H) and −3.9% for (R). Benzene yields were studied on different reconditioning methods applied to all catalysts: heating to 400° in air averaged 92.3%; the same temperature with a half and half mixture of O2 and Ar averaged 91.9%, adding a half and half mixture of H2 and Ar at 200° to the end of this treatment averaged 91.8%. Based on this research, the obvious difference seen between the catalysts is in their trace by-products.

A liquid scintillation counting apparatus that enables highly accurate measurements of 14C has been constructed at the Solar-Terrestrial Environment Laboratory, Nagoya University. The main aim of the project is high precision year-by-year measurements of the 14C content in tree rings of an old cedar tree from Yaku Island, Japan. We present the results of 14C measurements on tree rings from the Agematsu region for recent decades to confirm the validity of the system.

We have worked in collaboration with the Westinghouse Savannah River Company and Packard Instrument Company to develop a prototype instrument for remote, near real-time, in situ analysis of environmental levels of tritium in surface and ground water samples. The unit consists of a Packard Radiomatic™ 525TR liquid scintillation counter that has been modified to achieve lower detection levels through background reduction using Packard's After-Pulse Burst Discrimination electronics and an auxiliary Bi4Ge3O12 scintillation detector guard. The system is fully programmable to enable remote calibration, sample collection, sample analysis, reconfiguration of operational mode and interrogation for analytical results.

We present results that demonstrate the potential of the Packard Tri-Carb® Model 2770TR/SL for radiocarbon dating. For 2 g of sample benzene, a stable background count rate of 0.307 cpm and a stable counting efficiency of 64.78% were determined using a 13–75 keV counting window. Changes to the mathematical routines for t-SIE (quench indicating parameter) calculation and a reduction in the activity of the external standard have enabled stability of the t-SIE to be achieved, and combined with the use of a suitable balance point counting window; all of these factors give the stability of performance required for 14C dating. Calculations based on the above parameters indicate that the limit of detection for 2 g samples, counted for 5000 min, is >48,900 yr bp. The great advantage of this system is that these data were acquired using inexpensive standard 7-mL low potassium borosilicate glass vials. Vial holders manufactured from BGO reduced the background to 0.15 cpm with a minimum effect on efficiency (64.46% for 13–75 keV). A similar calculation of the limit of detection gave >51,700 bp. The use of the BGO vial holders in other instruments employing time-resolved liquid scintillation counting (TR-LSC) (Models 2250CA and 2260XL) also brought about significant improvements in detection limits.

In 1994, the Gliwice Radiocarbon Laboratory began operating a liquid scintillation spectrometry system, consisting of a Quantulus 1220™ spectrometer and two vacuum rigs for benzene production. This paper describes the procedures used for the benzene synthesis from samples containing < 1 g of carbon and in the range 1 to 10 g of carbon. We also present the Quantulus calibration procedures used in the Gliwice Radiocarbon Laboratory and NERC Radiocarbon Laboratory, and compare the calibration parameters.

In this paper we describe and discuss the advantages from improvements in equipment design and operating procedures developed at the State Scientific Centre of Environmental Radiogeochemistry (SSCER) laboratory in Kiev. Two experimental areas are considered, viz.

1. The direct chemisorption into a lithium alloy of carbonaceous gases produced by the controlled thermal degradation (pyrolysis) of organic materials under vacuum. This approach offers the advantage of a single stage, highly efficient and economical procedure for the production of lithium carbide. It is applicable for most types of sample material encountered in routine dating work and including organic detritus dispersed in a highly (up to 95% by weight) mineral matrix and/or carbonates. Bone collagen can also be processed without the need for its prior extraction and purification.

2. A conical thin walled reaction vessel for achieving improved and reproducible recoveries in the production of lithium carbide from CO2gas. This apparatus allows a much improved control over the surface dependent reaction in instances where there is no option other than the direct interaction of molten lithium with prepared CO2 gas.

In AMS measurements on small (m 400 μg) carbon samples, an m-dependence has been noted for the 14C/12C and 13C/12C ratios that is due to the combined effect of contamination and fractionation. A simple formalism is presented to describe the phenomena and to correct measurements on unknowns for their effect.

The majority of samples processed at the National Ocean Sciences AMS Facility (NOSAMS) thus far were collected as part of the World Ocean Circulation Experiment (WOCE). Due to the long storage time (2–3 yr) required to analyze thousands of samples on the accelerator mass spectrometer (AMS), a test was designed and implemented to determine the effects, if any, of storage time on 14C concentration. We find no systematic offsets in AMS measurements made over a 5-yr period between a total of 16 replicate sets from surface and deep water collected at the same locality. Furthermore, the average δ14C value from the deepwater AMS replicates (-213.1%, std. dev. 7.3) agrees very closely with the conventional 14C results published for GEOSECS (-212.7%) from station 320 taken 20 yr earlier.

A total of 73 WOCE shipboard replicate sets (162 AMS measurements) were analyzed with a mean precision of 4.3%. AMS results from 20 more shipboard replicate sets (44 AMS measurements) submitted as CO2 from the Stable Isotope Laboratory (SIL) at the University of Washington were analyzed with a mean precision of 3.4%. These results suggest no significant difference between water stripping methods used in each preparation lab.

To assess reproducibility, we calculate a pooled estimate of σ for replicates called s, which we use as an approximation of σTOT for a given sample type. The s for WOCE seawater replicates is 4.9% and 5.8% for SIL gas replicates. These numbers demonstrate an overall reproducibility of seawater AMS results at NOSAMS that is in line with reported errors. We take the difference between total error s and machine error as the overall standard deviation of combined uncertainties associated with preparation of samples and with AMS. For seawater samples processed at NOSAMS, σSPL is calculated to be 2.4%, and for the SIL gas replicates it is 4.8%.

Reproducibility of samples prepared with an acid hydrolysis technique is demonstrated using 24 coral samples submitted in triplicate by Dr. R. G. Fairbanks of Lamont Doherty Earth Observatory. Seventy-two replicates were prepared and analyzed at NOSAMS with a mean reported precision of 1.2%. The pooled estimate s for the Fairbanks triplicates is 2.6%. We calculate a laboratory reproducibility uncertainty for coral hydrolysis samples of 2.2%.

In 1993, NOSAMS participated in the Third International Radiocarbon Intercomparison (TIRI) Study. We report here 60 AMS analyses of the six TIRI test materials, five of which are organic carbon samples, to validate sample-processing methods for organic carbon sample AMS analyses at NOSAMS.

We report here on the radiocarbon dating of sediment samples from Bavaria using the Erlangen accelerator mass spectrometry facility. The absolute time calibration of different sediment profiles, together with pollen analyses, should establish a better chronology of climate and vegetation during Holocene in Bavaria. For an enhanced reliability of sediment dating, we measured different fractions such as bulk sediments, pollen grains, macrofossils and humic acids. For these fraction, we describe the separation methods and conversion to sputter targets. Furthermore, we discuss the sample preparation for the dating of bones and present some results.

Since our first report on the performance of the Kiel accelerator mass spectrometry (AMS) system and our early work on sample preparation, systems have been built to improve the sample quality and throughput of the laboratory. Minor modifications were also made on the AMS system, mainly in order to reduce the amount of work and time needed to maintain the system in optimal condition. The design and performance of a 20-port reduction system, a pneumatic target press, and a remote alarm unit for the AMS system are discussed, along with an overview of the results obtained during the last year and the procedure used to obtain them. Statistical analysis shows that the contribution of the AMS system to the measuring uncertainty at our current level (0.3% for a modern sample) is negligible.

The NOSAMS facility at Woods Hole Oceanographic Institution has started to develop and apply techniques for measuring very small samples on a standard Tandetron accelerator mass spectrometry (AMS) system with high-current hemispherical Cs sputter ion sources. Over the past year, results on samples ranging from 7 to 160 μg C showed both the feasibility of such analyses and the present limitations on reducing the size of solid carbon samples. One of the main factors affecting the AMS results is the dependence of a number of the beam optics parameters on the extracted ion beam current. The extracted currents range from 0.5 to 10 μA of 12C− for the sample sizes given above. We here discuss the setup of the AMS system and methods for reliable small-sample measurements and give the AMS-related limits to sample size and the measurement uncertainties.

A newly operating accelerator mass spectrometry (AMS) facility such as VERA has to go through an extensive testing phase in order to establish optimal conditions for 14C measurements, especially in the field of archaeological samples where an overall precision of 0.5% is desirable.

We discuss the results of our measurements at the milligram carbon level as they relate to long-term stability, reproducibility, precision and isotope fractionation.

Accelerator mass spectrometry (AMS) at the milligram level is routinely performed, but it is difficult to go substantially below 100 μg of carbon. We discuss various approaches for sample preparation, machine operation and data evaluation, to meet the special requirements of 14C AMS measurements at the microgram-carbon level. Furthermore, we present first results obtained at the Vienna Environmental Research Accelerator (VERA) from 14C measurements of a snow sample from Gaithersburg, Maryland, USA, prepared at the National Institute of Standards and Technology (NIST).

14C dating with the new Vienna Environmental Research Accelerator (VERA) began with the age determination of a mummified marmot found in the Austrian Alpine region. Soft tissue and bones of the marmot were used for the investigation. For comparison, bone material from known-age samples was also processed and measured. These exercises showed that 14C dating with VERA is reliable, and since that time various samples from archaeological context have been dated.

We also studied the applicability of the 14C method in forensic sciences to determine the time of death of human individuals. 14C/12C measurements of samples from different organic human material (bone collagen, lipids from bone and bone marrow, hair) were performed and compared with the tropospheric “bomb peak” values to transform the measured ratios into “calibrated ages”. For specific substances with rapid turnover rates, this gives an estimate for the time of death of the individual. In our study, lipids and hair yield reasonable times of death, whereas the collagen fraction from bones, which has a relatively long turnover time, is not suitable for this purpose.

During the past two decades, accelerator mass spectrometry (AMS) has allowed major developments in many areas of geosciences and archaeology. In the near future, AMS should realize a similar potential in the field of biomedical research, leading ultimately to clinical applications. For such applications, the required instrument differs significantly from that presently used in the field of 14C dating. Whereas the needed accuracy and sensitivity is more than an order of magnitude less demanding than that for present state-of-the-art 14C instrumentation, the widespread acceptance of 14C AMS in biomedical research will require AMS spectrometers that are small, simple to operate and capable of handling CO2 samples. In order to satisfy these demands, HVEE has developed a compact 14C AMS spectrometer dedicated to biomedical research. The instrument consists of a compact accelerator with a footprint of 2.25 × 1.25 m and an ion source that features direct CO2 acceptance and optimal user friendliness. Having previously described the layout and design of the accelerator, we here discuss progress on the accelerator and present the design and first results of the CO2 ion source.

Previous results from remains of tusks, teeth and bones collected from Wrangel Island (Vartanyan et al. 1995) had given results in the range 3730 bp to 20,000 bp and the authors had concluded that “mammoths inhabited Wrangel Island for as long as 6000 yr after the estimated extinction on the Siberian continent”. There still remained the question of the earliest date for such remains. Further, the authors had noted such samples may present some difficulty in dating and therefore duplicate samples had been measured in a second laboratory with satisfactory results. The replicate dating of important or controversial samples in more than one laboratory is well-established (e.g., Turin Shroud) and in this paper, we present results for 5 mammoth samples dated by 6 laboratories. Such interlaboratory comparisons provide an independent means of verification of laboratory comparability, and give added confidence in the results, particularly when applied to more controversial samples. A further objective of the work has been to evaluate the material for inclusion in any large-scale interlaboratory comparison, such comparisons having in the past formed part of laboratory quality assurance protocols. The design and organization of a laboratory intercomparison requires homogeneous samples in sufficient quantity to satisfy participants, and so in principle, a single mammoth tusk would meet these criteria. Samples such as the mammoth tusk have been used in previous intercomparisons: e.g., in the last large-scale international intercomparison (Gulliksen and Scott 1995), whalebone was one of the materials distributed. One of the key advantages of such material is that a single sample (a mammoth tusk) can be resampled for analysis by multiple labs and thus does not require bulk homogenization. Therefore, as part of a preselection process for a future intercomparison, five samples from separate mammoth tusks were collected from Wrangel Island in 1995 in sufficient quantity to allow multiple dating. The aim was to identify five separate samples of young age, sample up to 1 kg from each tusk and mark the location so that after preliminary dating, samples could be retrieved as required in the future. Six laboratories received samples for dating. The paper will discuss the results from the laboratories, present consensus values, and make recommendations concerning use of these samples in a future laboratory intercomparison.