Accelerator Mass Spectrometry Laboratory Research Articles

The André E. Lalonde AMS Laboratory – The new accelerator mass spectrometry facility at the University of Ottawa

The University of Ottawa, Canada, has installed a multi-element, 3MV tandem AMS system as the cornerstone of their new Advanced Research Complex and the principal analytical instrument of the André E. Lalonde Accelerator Mass Spectrometry Laboratory. Manufactured by High Voltage Engineering Europa B.V., the Netherlands, it is equipped with a 200 sample ion source, a high resolution, 120° injection magnet, a 90° high energy analysis magnet (mass-energy product 350MeV-AMU), a 65°, 1.7m radius electric analyzer and a 2 channel gas ionization detector. It is designed to analyze isotopes ranging from tritium to the actinides and to accommodate the use of fluoride target materials. This system is being extended with a second injection line, consisting of selected components from the IsoTrace Laboratory, University of Toronto. This line will contain a pre-commercial version of the Isobar Separator for Anions, manufactured by Isobarex Corp., Bolton, Ontario, Canada. This instrument uses selective ion–gas reactions in a radio-frequency quadrupole cell to attenuate both atomic and molecular isobars.This paper discusses the specifications of the new AMS equipment, reports on the acceptance test results for 10Be, 14C, 26Al and 127I and presents typical spectra for 10Be and actinide analyses.

Actinide measurements by AMS using fluoride matrices

Actinides can be measured by alpha spectroscopy (AS), mass spectroscopy or accelerator mass spectrometry (AMS). We tested a simple method to separate Pu and Am isotopes from the sample matrix using a single extraction chromatography column. The actinides in the column eluent were then measured by AS or AMS using a fluoride target matrix. Pu and Am were coprecipitated with NdF3. The strongest AMS beams of Pu and Am were produced when there was a large excess of fluoride donor atoms in the target and the NdF3 precipitates were diluted about 6–8 fold with PbF2. The measured concentrations of 239,240Pu and 241Am agreed with the concentrations in standards of known activity and with two IAEA certified reference materials. Measurements of 239,240Pu and 241Am made at A.E. Lalonde AMS Laboratory agree, within their statistical uncertainty, with independent measurements made using the IsoTrace AMS system. This work demonstrated that fluoride targets can produce reliable beams of actinide anions and that the measurement of actinides using fluorides agree with published values in certified reference materials.

Improving AMS Detection of the Biomedical Radiotracer 41Ca with Segmented Radio-Frequency Quadrupoles

41Ca is an important biomedical radiotracer finding many applications in biological, nutritional and medical studies. The detection of 41Ca by AMS is however limited by an important background signal of 41K originating from biological samples and from contaminated cesium in the source. An approach consisting of using PbF2-assisted in-source fluorination in combination with an Isobar Separator for Anions (ISA), a device incorporating a low energy radio frequency quadrupole (RFQ) gas cell, promises to push down the limit of detection of 41Ca attainable on small (<3 MV) accelerator mass spectrometry (AMS) systems by several orders of magnitude. Such on-line reduction of 41K should also result in a simplification of biological sample preparation and less concern about variable 41K contamination of the cesium beam. The selective collision-induced fragmentation of KF3− versus CaF3-, occurring in the gas cell of an ISA equipped with a double segment RFQ, have been reported earlier1), leading to K being suppressed by a factor of 1e4 over Ca. We present here the future configuration of the ISA, redesigned using multi-segmented RFQ to enhance further this effect and improve transmission through the gas cell. A segmented RFQ is an appropriate tool to finely control ion energy down to the few eV's separating the fragmentation energies of the two fluoride species. This pre-commercial ISA destined to be used at the newly established A. E. Lalonde AMS laboratory at University of Ottawa (Canada) will be presented. Some practicalities of integrating a low energy RFQ-based device in a high energy AMS system will also be discussed.

New single amino acid hydroxyproline radiocarbon dates for two problematic American Mastodon fossils from Alaska

American mastodon (Mammut americanum) was amongst the widest ranging of Pleistocene megafaunal species, though their fossils are rare in Alaska and northwest Canada. Questions remain about their extinction chronology at high latitudes because of the limited numbers of available radiocarbon dates. New radiocarbon dates for two American mastodon fossils were generated at two separate accelerator mass spectrometry laboratories using two different approaches, dating ultrafiltered ‘collagen’ vs. single amino acid fractions. The bulk dates for these specimens are significantly younger than the single amino acid (hydroxyproline) dates, which are in turn close to the background threshold for radiocarbon dating. On closer study we established that contamination from consolidants used in museum conservation was not removed thoroughly despite extensive physical and chemical cleaning procedures having been applied, and this led to the anomalous ultrafiltered ‘collagen’ results. The new hydroxyproline dates give support to older ages for American mastodons in the Arctic.

The Early to Late Paleolithic Transition in Korea: A Closer Look

In Korean Paleolithic archaeology, it is traditionally thought that the Late Paleolithic stone tool industries were in some way derived from the Shuidonggou site in northern China. The latter site has long been considered to be the type site of the eastern Asian Late Paleolithic blade technology. However, recent studies suggest that a number of Korean Late Paleolithic sites probably predate Shuidonggou, some by several thousands of years. Here, we present a series of accelerator mass spectrometry (AMS) dates recently analyzed by the AMS laboratory at Seoul National University and discuss further the possibility that the introduction of blade (and later microblade) technologies into Korea may have originated directly from Mongolia, Siberia, and possibly other areas of northeast China, rather than from Shuidonggou.

Recent progress in AMS measurement of 182Hf at the CIAE

In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for 182Hf/180Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of 180HfF−5 current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background 182W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.

Ultra-trace analysis of 36Cl by accelerator mass spectrometry: an interlaboratory study

A first international (36)Cl interlaboratory comparison has been initiated. Evaluation of the final results of the eight participating accelerator mass spectrometry (AMS) laboratories on three synthetic AgCl samples with (36)Cl/Cl ratios at the 10(-11), 10(-12), and 10(-13) level shows no difference in the sense of simple statistical significance. However, more detailed statistical analyses demonstrate certain interlaboratory bias and underestimation of uncertainties by some laboratories. Following subsequent remeasurement and reanalysis of the data from some AMS facilities, the round-robin data indicate that (36)Cl/Cl data from two individual AMS laboratories can differ by up to 17%. Thus, the demand for further work on harmonising the (36)Cl-system on a worldwide scale and enlarging the improvement of measurements is obvious.

Mass spectrometry with accelerators

As one in a series of articles on Canadian contributions to mass spectrometry, this review begins with an outline of the history of accelerator mass spectrometry (AMS), noting roles played by researchers at three Canadian AMS laboratories. After a description of the unique features of AMS, three examples, (14)C, (10)Be, and (129)I are given to illustrate the methods. The capabilities of mass spectrometry have been extended by the addition of atomic isobar selection, molecular isobar attenuation, further ion acceleration, followed by ion detection and ion identification at essentially zero dark current or ion flux. This has been accomplished by exploiting the techniques and accelerators of atomic and nuclear physics. In 1939, the first principles of AMS were established using a cyclotron. In 1977 the selection of isobars in the ion source was established when it was shown that the (14)N(-) ion was very unstable, or extremely difficult to create, making a tandem electrostatic accelerator highly suitable for assisting the mass spectrometric measurement of the rare long-lived radioactive isotope (14)C in the environment. This observation, together with the large attenuation of the molecular isobars (13)CH(-) and (12)CH 2(-) during tandem acceleration and the observed very low background contamination from the ion source, was found to facilitate the mass spectrometry of (14)C to at least a level of (14)C/C ~ 6 × 10(-16), the equivalent of a radiocarbon age of 60,000 years. Tandem Accelerator Mass Spectrometry, or AMS, has now made possible the accurate radiocarbon dating of milligram-sized carbon samples by ion counting as well as dating and tracing with many other long-lived radioactive isotopes such as (10)Be, (26)Al, (36)Cl, and (129)I. The difficulty of obtaining large anion currents with low electron affinities and the difficulties of isobar separation, especially for the heavier mass ions, has prompted the use of molecular anions and the search for alternative methods of isobar separation. These techniques are discussed in the latter part of the review.

Accelerator mass spectrometry

In this overview the technique of accelerator mass spectrometry (AMS) and its use are described. AMS is a highly sensitive method of counting atoms. It is used to detect very low concentrations of natural isotopic abundances (typically in the range between 10(-12) and 10(-16)) of both radionuclides and stable nuclides. The main advantages of AMS compared to conventional radiometric methods are the use of smaller samples (mg and even sub-mg size) and shorter measuring times (less than 1 hr). The equipment used for AMS is almost exclusively based on the electrostatic tandem accelerator, although some of the newest systems are based on a slightly different principle. Dedicated accelerators as well as older "nuclear physics machines" can be found in the 80 or so AMS laboratories in existence today. The most widely used isotope studied with AMS is 14C. Besides radiocarbon dating this isotope is used in climate studies, biomedicine applications and many other fields. More than 100,000 14C samples are measured per year. Other isotopes studied include 10Be, 26Al, 36Cl, 41Ca, 59Ni, 129I, U, and Pu. Although these measurements are important, the number of samples of these other isotopes measured each year is estimated to be less than 10% of the number of 14C samples.

Radiocarbon Sample Preparation at the Circe AMS Laboratory in Caserta, Italy

A system with several lines for the preparation of graphite targets for radiocarbon analysis has been built at the new accelerator mass spectrometry (AMS) facility in Caserta, Italy. Special attention has been paid in the design to the reduction of background contamination during sample preparation. Here, we describe the main characteristics of these preparation lines. Results of tests performed to measure 14C background levels and isotope fractionation in several blank samples with the Caserta AMS system are presented and discussed.

Measurements of natural levels of &lt;Superscript&gt;14&lt;/Superscript&gt;C in human's and rat's tissues by accelerator mass spectrometry in Korea

Accelerator mass spectrometry (AMS) is the most sensitive, safe and precise analytical method for quantifying long-lived isotope in biomedical research with animals as well as human beings. In Korea, AMS Laboratory has been operating successfully for years measuring especially archeological samples for 14C dating. In this year, a biological sample pretreatment facility was setup and we have also started to work on biomedical applications. As a preliminary study, we have measured the natural background levels of 14C in tissues and blood of humans and rats. The results were agreed with the other reported levels and gave stable and reproducible results within 1-2%.

Preparation of 26Al AMS standards

Absolute AMS (accelerator mass spectrometry) measurements require reliable standards for calibration. Highly concentrated 26Al was obtained from NBS (National Bureau of Standards). The 26Al, SRM 4229, was sequentially diluted with natural Al and 26Al AMS standards were prepared. These 26Al AMS standards are widely used as primary standards at major AMS laboratories. A substantial amount of 26Al AMS standards with 26Al/Al ratios of 7.444×10−11, 3.096×10−11, 1.065×10−11, 4.694×10−12, 1.818×10−12 and 4.99×10−13 are now available for the AMS community. Solutions having 26Al/Al ratios between 10−12 and 10−10 were measured by several AMS laboratories; excellent linearity was obtained within the range of 5×10−13–1×10−1026Al/Al.

The Keck Carbon Cycle AMS Laboratory, University of California, Irvine: Initial Operation and a Background Surprise

A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported 14C AMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.

Variability of Monthly Radiocarbon During the 1760S in Corals from the Galapagos Islands

Radiocarbon (Δ14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average Δ14C value of −62 is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760–1771 (±6 yr). High Δ14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low Δ14C values were obtained mid-year during strong upwelling. The average seasonal variability of Δ14C was 15–25, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high Δ14C values were found during 1762–1763 and 1766. A spectral analysis revealed that the spectral density for the Δ14C data displays most of its variance at the 5-yr cycle, which is reflective of El Niño periodicity during the 20th century.

The impact on archaeology of radiocarbon dating by accelerator mass spectrometry

Radiocarbon dating by accelerator mass spectrometry (AMS) differs fundamentally from conventional 14 C dating because it is based on direct determination of the ratio of 14 C : 12 C atoms rather than on counting the radioactivity of 14 C. It is therefore possible to measure much lower levels of 14 C in a sample much more rapidly than the conventional technique allows. Consequently, minimum sample size is reduced approximately 1000-fold (from ca . 1 g to ca . 1 mg) and the datable time span of the method can, theoretically, be doubled (from ca . 40 ka to ca . 80 ka). As yet, extension of the time span has not been achieved, because of the effects of sample contamination, but the great reduction in sample size is already having a major impact on archaeology by extending the range of organic remains that can be dated, and, especially, by allowing the archaeologist and the radiocarbon chemist to adopt more selective sampling strategies. This greater selectivity, in the field and the laboratory, is the most important archaeological attribute of AMS 14 C dating. It allows on-site chronological consistency to be tested by multiple sampling; archaeological materials to be dated that contain too little C, or are too rare or valuable, to be dated by the conventional method; and the validity of a date to be tested by isolating and independently dating particular fractions in chemically complex samples. AMS laboratories have only been processing archaeological samples since 1982, but already several, notably those at Oxford, Toronto, and Tucson, Arizona, have made substantial contributions to archaeological dating. The Oxford laboratory has, since 1983, processed ca. 1200 samples and published over 500 archaeological dates. Particular attention is therefore paid in this paper to the archaeological significance of the dates obtained at Oxford. The ams 14C technique can contribute to archaeological dating in two complementary ways: (i) by testing prevailing assumptions about the antiquity of indirectly dated objects and materials, i.e. verification or falsification dating; and (ii) by dating new or existing archaeological sequences in greater detail than can be achieved by the conventional 14 C technique, i.e. the building of new and more detailed chronologies. In this paper, recent archaeological applications of the new technique are reviewed under these two headings: verification dating applied to the origin and spread of anatomically modern humans in Europe and the Americas, to putative evidence for early (pre-Neolithic) agriculture in Israel and Egypt, and to the dating of rare Palaeolithic and later artefacts; and the building of new and more-detailed chronologies illustrated by reference to Upper Palaeolithic sequences in Europe, Mesolithic—Neolithic sequences in Southwest Asia, and Neolithic-Bronze Age chronologies in Britain. It is concluded that the development and application of the ams technique represents a revolution in 14 C dating that will have a profound impact on many aspects of archaeological research.