In recent years, High Voltage Engineering Europa (HVEE) has demonstrated its capability of developing and installing turnkey accelerator mass spectrometry (AMS) equipment for the analysis of, among others, 14C and 129I. Five 3MV systems using sequential and/or simultaneous injection are operational in the field today, and they have shown excellent long-term stability providing high-precision analyses on a routine basis. Another three AMS systems are in production. It is projected that for the time being, AMS will continue to broaden its field of applications; a saturation of the market of AMS facilities is not expected in the near future.

To meet the specific demands of the biomedical research community, we have developed an extreme compact 14C AMS system comprising a hybrid ion source capable of handling both graphite as well as CO2 samples. The source is optimized for easy maintenance, accommodates up to 200 samples, and can be implemented in any other AMS system.

More recently, HVEE has initiated the development of an AMS system capable of detecting, among others, 36Cl and 41Ca. The design will include a HVEE 5MV Tandetron™. The accelerator is currently under construction as part of an ion beam analysis system for the Universidad Autonoma de Madrid (Spain).

Radiocarbon measurements by two 1220 Quantulus™ ultra low background liquid scintillation spectrometers were performed at the underground laboratory of Gran Sasso and the Radiocarbon Laboratory of E.N.E.A.-Bologna to study the efficiency and background variations related to measurement sites. The same configuration setup, i.e. the same center of gravity of the 14C spectrum (SQP(I) = 410 ± 1) was obtained in both instruments. Many different background and modern standards with pure analytical benzene were used and spectra for 40 one-hour periods were obtained. The data indicates a background reduction of approximately 65% between the surface and underground laboratories, with no differences in the efficiency. Recording similar efficiencies in both spectrometers is probably due to fairly identical photomultiplier characteristics. The cosmic noise reduction observed at the laboratory of Gran Sasso makes it possible to perform high precision 14C measurements and to extend for these idealized samples the present maximum dating limit from 58,000 BP to 62,000 BP (5 mL, 3 days counting).

The accelerator mass spectrometry facility at the Seoul National University (SNU-AMS) was completed in December 1998 and a report was presented at the Vienna AMS conference in September 1999. At the conference, we described the basic components of our accelerator system and reported the results of the performance test. Since then, extensive testing of the accuracy and reproducibility of the system has been carried out, and about 200 unknown samples have been measured so far. We obtained a precision of 4‰ for modern samples, and an accuracy of approximately 40 yr was demonstrated by analyzing samples that were previously dated with a conventional technique and by other AMS laboratories. We present these results here, together with detailed descriptions of our data-taking and analysis procedures.

Measurements of the radiocarbon concentration of several carbonate background materials, either mineral (IAEA C1 Carrara marble and Icelandic double spar) or biogenic (foraminifera and molluscs), show that the apparent ages of diverse materials can be quite different. Using 0.07 pMC obtained from mineral samples as a processing blank, the results from foraminifera and mollusc background samples, varying from 0.12 to 0.58 pMC (54.0-41.4 ka), show a species-specific contamination that reproduces over several individual shells and foraminifera from several sediment cores. Different cleaning attempts have proven ineffective, and even stronger measures such as progressive hydrolization or leaching of the samples prior to routine preparation, did not give any indication of the source of the contamination. In light of these results, the use of mineral background material in the evaluation of the age of older unknown samples of biogenic carbonate (>30 ka) proves inadequate. The use of background samples of the same species and provenance as the unknown samples is essential, and if such material is unavailable, generic biogenic samples such as mixed foraminifera samples should be used. The description of our new modular carbonate sample preparation system is also introduced.

It is well known that, during the widely used AAA pretreatment (de Vries and Barendsen 1954), alkali treatment is responsible for the incorporation of modern carbon due to the precipitation of atmospheric CO2 as carbonate. Until now, the last step of the experiment, consisting in acid treatment (most of the time with hydrochloric acid) was considered to be sufficient to eliminate all of lab contamination. But wood, peat and sediment present a complex molecular structure. During radiocarbon chemical treatments, functional groups still present in the molecules are likely to form ionic bonds with “modern” carbonates. These new chemical bonds resist a “classical” acid treatment and are responsible for rejuvenation. This short paper presents preliminary results for two common 14C cases: rejuvenation of a 0.4 pMC wood and of an Oxygen Isotope Stage 3 (OIS3) paleosol. For both cases, contamination due to incorporation of modern carbon during chemical treatment is evaluated and an alternative protocol is proposed.

This study describes a sample preparation technique used to isolate dissolved organic carbon (DOC) in groundwater for radiocarbon analysis using accelerator mass spectrometry (AMS). The goal of the work is to improve our ability to determine groundwater residence times based on 14C measurements of the DOC fraction in groundwater. Water samples were collected from carbonate and volcanic rock aquifers in southern Nevada. Multiple measurements of total dissolved organic carbon (TDOC) in groundwater from one site are used to demonstrate the reproducibility of the analytical procedure. The reproducibility of the method is about one percent (1σ) for a 0.5 mg sample. The procedural blank for the same size sample contains about 1 percent modern carbon (pMC).

We have developed and demonstrated a practical methodology for dating specific compounds (and octade-canoic or stearic acid—C18:0—in particular) from the lipid material surviving in archaeological cooking pots. Such compounds may be extracted from about 10 g of cooking potsherd, and, after derivatization, can be purified by gas chromatography. To obtain sufficient material for precise dating repetitive, accumulating, GC separation is necessary. Throughout the 6000-year period studied, and over a variety of site environments within England, dates on C18:0 show no apparent systematic error, but do have a greater variability than can be explained by the errors due to the separation chemistry and measurement process alone. This variability is as yet unexplained. Dates on C16:0 show greater variability and a systematic error of approximately 100-150 years too young, and it is possible that this is due to contamination from the burial environment. Further work should clarify this.

Reliable radiocarbon dating depends upon well-defined samples. We have been investigating whether or not reliable 14C dates can be obtained directly from sub-fossil insect cuticle or biochemical fractions derived from it. Initial carbon and nitrogen stable isotope measurements on sub-fossil insect chitin from species with known feeding behaviors found within a single site (St Bees, Cumbria) clustered in a manner reminiscent of trophic level effects seen in terrestrial ecosystems. Although this finding implied some chemical stability, the measurement of CN ratios from the same samples indicated compositional variability. In addition, 14C dates obtained from these same samples were different from dates obtained from plant macrofossils found at the same depth. We have experimented with protocols designed to biochemically reduce chitin to its principle carbohydrate component glucosamine with the aim of using this compound to generate reliable 14C dates. Solvent extractions of sub-fossil chitin were carried out to remove both endogenous and exogenous lipid-soluble materials. Base hydrolysis reactions designed to extract polypeptides retained surprisingly high levels of contaminating amino acids. Proteinase K enzyme treatment had little affect on the level of amino acid contamination. Strong acid hydrolysis reactions designed to depolymerize chitin to glucosamine yielded only 5% glucosamine. Clearly alternative methods of chitin depolymerization must be identified before the purification and 14C dating of glucosamine from sub-fossil chitin becomes practical.

Preliminary experiments were carried out on archaeological wood to investigate methods of cellulose hydrolysis and carbohydrate monomer purification for the purpose of compound-specific radiocarbon dating. The Chelford log, a known 14C dead source of wood cellulose, was selected for study in order to investigate the levels of contamination introduced during sample purification. Two methods of hydrolysis were examined, mineral acid hydrolysis and enzyme hydrolysis using cellulase from Penicillium funiculosum. Under the conditions described, enzymolysis was far superior to acid hydrolysis in terms of the glucose monomer yield. Glucose monomer purification was accomplished using high pH anion exchange chromatography with pulsed amperometric detection. This high performance liquid chromatography (HPLC) method does not require sample derivatization and the chromatography products can be collected in water. These characteristics make it potentially well suited to carbon dating applications. 14C dating of chromatographically purified glucose fractions revealed significant levels of contamination had accumulated during both protocols. Glucose contamination from the cellulase enzyme preparation was a major source of contamination within the enzymatically hydrolyzed samples. Ultrafiltration of the enzyme removed some but not all of this contamination. The contamination must be reduced 10-fold before the methodology could be viable for dating. This hydrolysis/HPLC method is also being investigated for 14C dating of other carbohydrate polymers such as chitin.

We present the current status of accelerator mass spectrometry (AMS) dating of iron artifacts at Seoul National University (SNU). In ancient iron production, charcoal was widely used as carbon for the smelting process, whereas coal is used in modern times. If reliable data could be obtained from carbon by using AMS, ancient iron artifacts could be traced to their production age. In normal acid treatment, it is not easy to extract carbon due to its colloidal property. The negative charge property of the carbon colloid, however, makes it possible for it to be precipitated with positive ions by dissolving the iron chemically. An extraction yield of the carbon incorporated in modern cast iron of about 70% is attained. More refined methods to increase the extraction rate are under progress for archaeological applications.

A new sealed double tube combustion method was developed at Lawrence Livermore National Laboratory (LLNL) to extract carbon from modern steels and ancient iron artifacts. Iron samples were chemically pretreated with 10% nitric acid, vacuum sealed in 6 mm quartz tubes with CuO, vacuum sealed again inside 9 mm quartz tubes, and combusted at 1000 °C for a minimum of 10 hr. The resulting CO2 was graphitized routinely using hydrogen reduction (Vogel et al. 1989). After the initial phase of development, carbon yields of 100% were consistently obtained. The activities of two modern high carbon steels (treated as process blanks, manufactured using only coal as the carbon source) were determined to be 0.0077 ± 0.0009 (n = 12, ± 1 σ) for a 1.3% C steel and 0.0090 ± 0.0038 (n = 12, ± 1 σ) for a 1.9% C steel, indicating that very little contamination is introduced during the sample preparation process. Since the Iron Age began less than 5000 years ago, these background uncertainties should introduce errors of no more than ±30 years to the radiocarbon ages of actual artifacts. Two ancient iron artifacts of known date were analyzed and demonstrate that the new methodology can be used to obtain the correct date of manufacture for iron objects, provided that they are made exclusively using charcoal that was contemporaneous with the manufacture of the artifact. Since only 1 mg of carbon is required for accelerator mass spectrometry (AMS), very small iron samples can now be analyzed (50 mg of a 2.0% C iron or 1 g of a 0.1% C iron). We anticipate that this methodology will be particularly useful to archeologists who currently have to rely on context to date iron artifacts.

At the Leibniz radiocarbon lab, art and archaeological objects, often chemically conserved and thus potentially contaminated with respect to their 14C content, are treated using a computer-controlled “Soxhlet”-type series extractor. This device uses a continuous procedure of boiling and condensation of different solvents for extraction and vacuum filtration under constant process conditions. An elutrope sequence of five solvents that dissolve most customary conservation chemicals was selected. A study of these different contaminants applied to reference wood samples with subsequent accelerator mass spectrometry (AMS) measurements demonstrates that their effective removal is dependent on the use of adequate solvents. For many contaminants (e.g. wood glue, methyl cellulose, Klucel®, sugar, and polyethylene glycol), routine acid-alkali-acid (AAA) treatment already yields satisfactory results, whereas for Caparol® and beeswax a relatively “mild” treatment with acetone, methanol, water, and subsequent standard AAA extraction is sufficient. Complete removal of rubber glue, epoxy resin, and paraffin can only be accomplished with our full set of solvents. The latter procedure is also appropriate when no or only incomplete information about the type of conservation material is available. For epoxy resin the contamination appears to be enriched in the alkali residue, and the easily soluble “humic acid” fraction, even after standard AAA treatment, gives satisfactory results. Two case studies on the application of the extraction procedures are presented.

We compare radiocarbon accelerator mass spectrometry (AMS) ages of wood samples subjected to a conventional acid-base-acid pretreatment with stepped combustion (ABA-SC) with results from the same samples subjected to an acid-base-wet oxidation pretreatment with stepped combustion (ABOX-SC) and cellulose extraction with stepped combustion (CE-SC). The ABOX-SC procedure has been shown previously to lead to lower backgrounds for old charcoal samples. Analyses of relatively uncontaminated “14C-dead” samples of wood suggest that backgrounds of 0.11 ± 0.04 pMC are obtainable for both the ABOX-SC and ABA-SC procedures. Where wood is significantly contaminated the ABOX-SC technique provides significantly better decontamination than either the ABA-SC technique or cellulose extraction alone, although CE-SC can produce comparably low backgrounds to the ABOX-SC procedure.

We also report the application of the ABOX-SC, ABA-SC and CE-SC procedures to wood samples associated with the chronologically controversial Rotoehu Ash eruption, New Zealand. New 14C-AMS dates from wood sampled from below the Rotoehu Ash span an age range of 43–50 ka BP consistent with recently presented OSL dates of 42–44 ka obtained for palaeosols beneath the ash.

When dating unburnt bone, bone collagen, the organic fraction of the bone, is used. Collagen does not survive the heat of the cremation pyre, so dating of cremated bone has been considered impossible. Structural carbonate in the mineral fraction of the bone, however, survives the cremation process. We developed a method of dating cremated bone by accelerator mass spectrometry (AMS), using this carbonate fraction. Here we present results for a variety of prehistoric sites and ages, showing a remarkable success rate for this method.