Abstract Accelerator Mass Spectrometry Research Articles

EARLY HOLOCENE OXYGEN ISOTOPE CHRONOLOGIES (11,267–6420 CAL BP) FROM ICE WEDGE AT CHARA, TRANSBAIKALIA

ABSTRACTAccelerator mass spectrometry radiocarbon (AMS 14C) dating was used for determining the age of wedge ice. It has been found that between 11,270 and 6420 cal BP, or the Greenlandian and Northgrippian stages of the Holocene, ice wedges grew syngenetically in sandy deposits with gravel in the Chara River valley. The variations of δ18O values in the ice wedges are about 8‰, from –25.5‰ to –18.8‰. Based on the stable isotope composition of ice wedges, paleotemperature reconstructions revealed that the mean January temperature was as low as –38°C during the coldest periods of the early half of the Holocene and as high as –28°C during the warmer periods.

ACHIEVING LOW BACKGROUNDS DURING COMPOUND-SPECIFIC HYDROXYPROLINE DATING: HPLC COLUMN EFFECTS

ABSTRACT Accelerator mass spectrometry (AMS) radiocarbon (14C) dating is central to the development of robust chronologies in archaeological and paleoenvironmental contexts spanning the last 50,000 years. For dates to be accurate, samples must be free of exogenous carbon contamination. At the Oxford Radiocarbon Accelerator Unit (ORAU), considerable advancements in the dating of bone collagen have been made through the development of a high performance liquid chromatography (HPLC) method for the dating of the amino acid hydroxyproline, which can mitigate the effects of carbon contamination. However, recent changes in ligand manufacturing methods for the mixed-mode column used in the ORAU protocol (Primesep A, SIELC Technologies; IL, USA) have resulted in unacceptably high analytical backgrounds. Prior to the manufacturing change, backgrounds of > 50k BP were achievable. Since the manufacturing change, a mean background of 32.5k BP has been measured. Due to column bleed, the Primesep A is therefore no longer suitable for 14C measurement of hydroxyproline from older material. Here, we present background data and the chromatography conditions used to isolate hydroxyproline using an alternative column, a preparative-scale Newcrom AH, which shows promising potential as an alternative for the routine isolation and AMS dating of hydroxyproline—especially approaching the age and mass limits of the method.

REFINING CERAMIC CHRONOLOGY AND EPICLASSIC REOCCUPATION AT LA VENTILLA, TEOTIHUACAN USING TRAPEZOIDAL BAYESIAN MODELING

ABSTRACTAccelerator mass spectrometry radiocarbon (AMS 14C) dates (n = 78) from human bone collagen were analyzed in the largest high-resolution chronology study to date at the ancient city of Teotihuacan in central Mexico (ca. AD 1–550). Samples originate from the residential neighborhood of La Ventilla, located in the heart of this major urban center. Here, a trapezoidal model using Bayesian statistics is built from 14C dates combined with data derived from the stylistic analysis of ceramics from burial contexts. Based on this model, we suggest possible refinements to Teotihuacan’s ceramic chronology, at least within the La Ventilla neighborhood. We also explore the abandonment and reoccupation of La Ventilla after the political collapse of Teotihuacan in the Metepec and Coyotlatelco phases. Findings suggest that these ceramic phases began earlier than is currently projected and that the well-documented abandonment period of La Ventilla may have occurred more abruptly than originally estimated.

Everything is a question of time – age of important Quaternary palaeontological finds from Westphalia

Accelerator mass spectrometry (AMS) was used to establish the age of three mammal specimens from the Quaternary of the Münsterland, North Rhine-Westphalia, Germany. The dated samples represent regionally important finds: The woolly mammoth from Ahlen with an age of 41 ka BP and the musk-ox from Herne with an age of 24 ka BP are typical representatives of the so-called mammoth steppe. The European Bison from Gladbeck with an age of 9.2 ka BP confirms the Early Holocene appearance of this species in Europe.

Biological and biomedical 14C-accelerator mass spectrometry and graphitization of carbonaceous samples

Accelerator mass spectrometry (AMS) is the ultimate technique for measuring rare isotopes in small samples. Biological and biomedical applications of (14)C-AMS (bio-(14)C-AMS) commenced in the early 1990s and are now widely used in many research fields including pharmacology, toxicology, food, and nutrition. For accurate, precise, and reproducible bio-(14)C-AMS analysis, the graphitization step in sample preparation is the most critical step. So, various sample preparation methods for a process called graphitization have been reported for specific applications. Catalytic graphitization using either a flame-sealed borosilicate tube or a septa-sealed vial is a popular sample preparation method for bio-(14)C-AMS. In this review, we introduce the AMS system, especially for bio-(14)C-AMS. In addition, we also review the graphitization method for bio-(14)C-AMS to promote further understanding and improvement of sample preparation for this technique. Examples of catalytic graphitization methods over the past two decades are described.

Challenging Developments in Three Decades of Accelerator Mass Spectrometry at ETH: From Large Particle Accelerators to Table Size Instruments

Accelerator mass spectrometry (AMS) was invented for the detection of radiocarbon at natural isotopic concentrations (10(-12) to 10(-15)) more than 30 years ago. Meanwhile this method has also been applied for the analysis of many other long-lived radioisotopes, which are found at very low concentrations. The first investigations were made at large tandem accelerators originally built for nuclear physics research and operating at voltages of 6-12 MV. Today dedicated instruments are mostly used for AMS, which are optimized for associated applications. In the past 15 years, a new generation of much smaller instruments has been developed. For many years it was believed that accelerators with voltages of 2 MV or higher are needed to eliminate the molecular interferences. At these energies the ions are predominantly stripped to charge state 3+, thereby removing the binding electrons of the molecules. In contrast, the new compact facilities use 1+ or 2+ ions. In this case the molecular destruction process is based on molecule-atom collisions in the gas cell. The cross sections for this destruction are sufficiently large that the intensity of molecular components such as (12)CH(2) and (13)CH can be reduced by 10 orders of magnitude. These new facilities can be built much smaller due to the lower energies. Universal instruments providing analysis for many isotopes over the whole range of periodic table have a space requirement of about 4 x 6 m(2); dedicated radiocarbon facilities based on a 200 kV accelerator have a footprint of about 2.5 x 3 m(2). This smallest category of instruments use special technologies: The high voltage terminal with the gas stripper canal is vacuum insulated and the gas is pumped to ground potential through a ceramic pipe. A conventional 200 kV power supply provides the terminal voltage from outside. A review of this new generation of compact AMS facilities is given. Design considerations and performance of these new instruments will be presented. With these developments, new AMS instruments are not much larger than conventional mass spectrometers, allowing a significant reduction in cost.

Simultaneous AMS determination of 14C content and total carbon mass in biological samples

Abstract Accelerator Mass Spectrometry (AMS) is now recognized as one of the most powerful techniques available for conducting ultrasensitive clinical studies. However, since for biological applications the relevant quantity is the total 14 C activity (i.e. dpm/mL sample), AMS 14 C measurements must be combined with total carbon concentrations measured on a separate instrument using a different sample aliquot. This procedure is inherently a source of large inaccuracies, especially in non-homogeneous samples such as urine and fecal blends. To overcome this limitation we developed a new measurement technique whereby a small amount of 13 C-enriched carbon carrier is added to each sample. Accurate measurement of the 13 C/ 12 C and 14 C/ 13 C ratios of the mix can be used to simultaneously calculate total carbon mass and 14 C concentration of the original sample. In this paper we present our first test runs including a detailed error analysis demonstrating that sample mass and 14 C concentration of the original sample can be determined with a precision and accuracy of better than 3%, thus significantly reducing the final uncertainty due to sample in-homogeneities.

A New 6MV Accelerator Mass Spectrometer for the University of Cologne

Accelerator Mass Spectrometry (AMS) is a technique to measure long-lived radioisotopes with very high sensitivity. The radioisotopes can be of natural origin such as cosmogenic nuclides produced by cosmic rays or of anthropogenic origin such as nuclides produced in nuclear fuel processing. Since its development in 1977 AMS has revolutionized the field of radionuclide dating. There is nowadays a wide range of applications for AMS in various fields like earth and ocean sciences, archaeology, hydrology, pollution studies, biochemistry and biomedicine [1].

Applications of14C-AMS in biomedical sciences (Bio-14C-AMS)

Accelerator mass spectrometry (AMS) is an ultrasensitive measure for tracing14C labeled moleculesin vivo or detecting the biomarker for assessment of carcinogenesis. In this review, basic principles, wide applications and new progresses of14C-bio-AMS are presented. It has been a new advanced tool for measuring the adduction of biologcial molecules with xenobiotics, including carcinogens, drugs, agrochemicals, nicotine, etc. The successful applications have proven the effectiveness of AMS to assessing cancer risk, screening drug toxicity and studying nutrients uptake. In particular, AMS is characterized by measuring xenobiotics at very low dose levels relevant to human environmental exposure. It is sensitive and precise to an attomole (10−18 mole) or less of14C per mg carbon. Although it has some shortcomings, undoubtedly, AMS possesses an evident merit of high sensitivity and will have widespread applications in the biomedical sciences.

Measurement of 237Np in environmental water samples by accelerator mass spectrometry.

Accelerator mass spectrometry (AMS) was used to measure 237Np in environmental water samples extracted from Irish Sea sediments. The samples were of limited volume (approximately 700 ml) and of low activity (0.06-0.79 mBq l-1; 2.30-30.3 pg l-1). AMS proved to have the required sensitivity for measuring these samples, and was in principle capable of measuring much smaller amounts, as low as 0.4 microBq (3.9 x 10(7) atoms). However, the background level in the procedural blanks showed that there was a systematic low level 237Np contamination of each sample, arising from the 239Np yield monitor used in the separations procedure, which effectively increased the detection limit of these analyses.

Detection of99Tc by accelerator mass spectrometry: Preliminary investigations

Accelerator mass spectrometry (AMS) is an established technique for the detection of long-lived radionuclides at environmental levels. At LLNL, planned facility upgrades and advances in detection techniques are allowing us to explore the applicability of AMS to isotopes not previously pursued. One such isotope is99Tc. We have performed a number of preliminary tests to examine the technical feasibility of AMS for the detection of99Tc. The questions addressed were negative ion production in the cesium sputter source, transport efficiency for the ions through the spectrometer, and detection efficiency for99Tc ions after the spectrometer. Based on the positive results of these tests, we have begun to develo measurement protocol.

Late-glacial – early Holocene vegetation, climate, and fire at Sutherland Pond, Hudson Highlands, southeastern New York, U.S.A.

Accelerator mass spectrometry dated pollen, plant-macrofossil, and charcoal records from Sutherland Pond (41°23′29″N, 74°02′16″W), located in the Black Rock Forest, provide a detailed account of forest history during the late-glacial – Holocene transition in the Hudson Highlands, lower Hudson Valley, southeastern New York. Pollen assemblages dating more than 12 600 radiocarbon years before present (years BP) are dominated by herbaceous and shrub types (Salix, Betula, Alnus, Ericaceae, Cyperaceae, Gramineae, and Tubuliflorae), with some arboreal types (Pinus and Picea), apparently representing an open landscape possibly with scattered trees. At 12 600 years BP increased organic deposition and pollen influx and the first occurrence of macrofossils indicate dramatic environmental change. Mixed assemblages of boreal and temperate taxa (Picea, Abies, Betula papyrifera, Quercus, Ostrya – Carpinus, and Fraxinus) are evident from 12 600 to 11 200 years BP. Low charcoal influx suggests that fire was a minor component of early woodland development beginning around 12 600 years BP. A Picea–Abies–Alnus assemblage, suggesting a cool climatic episode, dominates between 11 200 and 10 120 years BP, with rapid onset and termination each occurring within 150 years. Fire activity is also low during this colder interval. Warmer conditions, reestablished by 10 120 years BP, are inferred from expansion of Pinus strobus and increasing Quercus and Ostrya–Carpinus, followed by replacement of B. papyrifera by Betula populifolia and increased charcoal influx. Key words: late glacial, pollen, plant macrofossils, fire, accelerator mass spectrometry radiocarbon dating, New York.

14C AMS measurements from the Late Weichselian part of the Swedish Time Scale

Abstract Accelerator mass spectrometry measurements on plant macrofossils from the older part of the Swedish Time Scale, a chronology spanning over the past 13,000 calendar years, indicate a good agreement between varve years and calibrated ages (tree-rings, UTh) between ca. 10,500 and ca. 12,000 calendar years BP. Around 12,000 varve years, the varve/radiocarbon discrepancies seem to reach a maximum, while the UTh/radiocarbon differences increase steadily.

Latest Pleistocene lake shorelines and glacial chronology in the Western Basin and Range Province, U.S.A.: insights from AMS radiocarbon dating of rock varnish and paleoclimatic implications

Accelerator mass spectrometry radiocarbon dating of organic matter in the basal layer of rock varnish provides a minimum surface exposure age for the underlying landform. Varnishes 14C ages indicate that the latest Pleistocene highstand of Lake Lahontan was abandoned before 12.7 ka, Searles Lake before 13.6 ka, Lake Manly before 13.0 ka, and Lake Mojave before 11.6 ka. The maxima of the Tioga glaciation at Pine Creek in the eastern Sierra Nevada, California, and the Middle Creek glaciation in the adjacent White Mountains of California-Nevada was just before 18–19 ka; major recessional moraines were deposited in these ranges before 12–13 ka. Penecontemporaneous glacial retreat and high levels in closed-basin lakes cannot be explained by glacial melt water, but probably reflects higher snowlines and more precipitation. A relatively minor glacial advance, perhaps related to the “Younger Dryas” in Europe, may be penecontemporaneous with a slight transgression in lake levels about 10–11 ka in the western Basin and Range, suggesting a temporary return to cooler or wetter conditions, or both at the termination of the Pleistocene.

The archaeology of radiocarbon accelerator dating

Accelerator mass spectrometry (AMS) allows radiocarbon dating to be carried out by direct counting of14C atoms, rather than the conventional counting of radioactive disintegrations. The result is that samples up to 1000 times smaller can be handled. The approach was tested in principle by 1977 and for archaeological operation by 1983. More than 2000 samples per year are now being dated worldwide. The machines can now operate to about ± 80 years or better. Dates older than 40,000 years have not yet been achieved, but the ability to use small samples has already had considerable impact on dating the period 10,000–30,000 years ago. Bone is an ideal material for the new technique, since amino acids can normally be isolated and purified from gram-size samples. Studies of the origins of domestication are aided by the dating of individual grains and seeds. Because small samples can be mobile in the soil, careful sample selection strategies and procedures are required. The full impact of the technique can be assessed only through the rapid and comprehensive publication of archaeological results.

Accelerator radiocarbon date confirms early deglaciation of the Queen Charlotte Islands

Accelerator mass spectrometry was used to test whether part of eastern Graham Island was ice free at the height of late Wisconsin glaciation on mainland British Columbia. An accelerator radiocarbon date of 14 700 ± 700 years on a small twig conforms with two conventional dates that suggested that the Cape Ball region of Graham Island was deglaciated by about 15 000 radiocarbon years ago.

14C dating of small archaeological samples: neolithic to iron age in the central alpine region

Accelerator mass spectrometry (AMS) radiocarbon 14C dating will widen enormously the range and scope of archaeological investigations. This is due mainly to 100- to 1000-fold sample size reduction over conventional dating. In order to determine the size and the quality of samples that can be accepted for AMS 14C dating, we have selected archaeological samples relating to the Neolithic to Iron Age. The basis of our AMS target preparations is the coking (pyrolysis) of organic matter after elimination of impurities by various physical and chemical treatments. The effect of the morphology as well as of the grain size distribution of the charcoal particles was determined in order to achieve optimal conditions for accelerator dating.

Accelerator mass spectrometry at Chalk River

Accelerator mass spectrometry of 14C was studied with the Chalk River MP tandem from 1978 until the tandem was shut down in 1982 for the installation of a post-accelerator. The performance of the original system is reviewed and plans for AMS with the new accelerator facility are presented.