Accelerator Mass Spectrometry Measurements Research Articles

Characterization of meteoric 10Be in certified reference materials for use in internal control standards

In recent decades, interest in the measurement of 10Be has increased due to its relevance in various fields of science. Trace amounts of 10Be produced from meteoric sources require sensitive accelerator mass spectrometry (AMS) measurements and robust sample preparation. The extraction, separation, and preparation of the appropriate oxide form for AMS require extensive and careful laboratory processing and certified reference materials to validate the chemical performance of the protocols used and the calibration of the AMS system in the measurement. In this work, the meteoric 10Be concentrations in two certified reference materials are characterized to establish their suitability as internal control standards for laboratory chemical preparation and AMS measurements of this radioisotope in our laboratory and the whole AMS community.

Accelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site

Low-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 233U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites.

Quantification of 239Pu radioactivity in swipe samples by accelerator mass spectrometry

In the AMS Laboratory at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH) in Bucharest, Romania plutonium measurements started a few years ago. In the course of this period, we chemically processed environmental samples that could have contaminated the laboratory with 239Pu in the femtogram range. Swipe samples taken in the sample processing laboratory were investigated to quantify the potential plutonium contamination. Following the accelerator mass spectrometry measurements, the limit of detection for 239Pu in the order of 1 fg was determined, while the amount of 239Pu in the swipe samples was around 2 fg. The chemical procedure and the AMS measurement were validated by analyzing simulated swipe samples as a part of a proficiency test organized by the International Atomic Energy Agency. The obtained results show that the 1MV AMS system at IFIN-HH can be routinely used for determination of 239Pu concentrations in environmental matrices.

Coulomb explosion of BeO− molecular ions – Revisited

Accelerator mass spectrometry (AMS) measurements of 10Be almost invariably utilize the BeO- molecular negative ion. Molecular ions experience the process of ‘Coulomb explosion’ when dissociated by a stripper in the high-voltage terminal of a tandem accelerator, resulting in energy and angular spread of the subsequently-accelerated positive ions. In this paper, the phenomenon is studied in detail for both foil and gas stripping of BeO, using the 14UD pelletron accelerator at the Australian National University operating at 8.5 MV. In a companion paper by Suter et al. [1], a model is developed to interpret, inter alia, these results.

Determination of 129I in waters associated with coalbed methane using solvent extraction and accelerator mass spectrometry measurement

Determination of 129I in waters associated with coalbed methane using solvent extraction and accelerator mass spectrometry measurement

Preparation of new 10Be and 26Al AMS standard reference materials

Accelerator Mass Spectrometry (AMS) measurements require reliable standards for calibration. Beryllium-10, 26Al, 36Cl, and 41Ca AMS standards that were prepared by the author are used as primary normalization standards in most AMS laboratories worldwide. The expansion of applications and AMS facilities, accordingly an increase in sample measurements, over the last three decades has largely depleted the available stock of 10Be and 26Al standards that were prepared in 2001 as a series known as the “2001 or 01 dilution”. We have undertaken the task of making a new series of 10Be and 26Al AMS Standard Reference Materials (SRM) (“2014 or 14” series) that were prepared from the same parent solution used to produce the 2001 standards. Seven different concentrations of 10Be AMS standards were prepared from a stock solution 2001-4 by sequential dilution with (∼10 kg of) 36.5 mg Be/g carrier solution. The 10Be/Be ratios of the new standards are 1.01 × 10−13, 5.02 × 10−13, 2.507 × 10−12, 2.508 × 10−12, 7.523 × 10−12, 1.504 × 10−11, and 2.502 × 10−11. Six different concentrations of 26Al AMS standards were prepared from a stock solution 2001-3 by sequential dilution with a 35.7 mg Al/g carrier solution. The 26Al/Al ratios of the new standards are 1.51 × 10−13, 5.01 × 10−13, 2.501 × 10−12, 7.501 × 10−12, 1.500 × 10−11 and 5.000 × 10−11. Both 10Be/Be and 26Al/Al ratios of the new 2014 SRM were measured by five AMS laboratories; excellent linearity as well as agreement with the 2001 standard were observed. New 2014 10Be and 26Al SRM are available for the AMS community and are being distributed in the same way as the 36Cl and 41Ca SRM.

Relative formation probabilities for fluoride and oxyfluoride anions of U, Np, Pu and Am in accelerator mass spectrometry measurements at VERA

Fluoride molecular anions have emerged as a potential alternative to oxides for the analysis of actinides in AMS. Research at the Vienna Environmental Research Accelerator (VERA) has focused on mixing samples prepared in an Fe2O3 matrix with PbF2 for in situ fluoridation during the sputter process. The relative formation probabilities for a range of (oxy-)fluoride molecular anions of uranium, neptunium, plutonium, and americium have been found to be characteristic for each of the actinides investigated. These data can help to identify isobaric interference for the mentioned actinides. A first application is monitoring of the 236U co-production with 236Np during Th irradiation. Extracting these actinides in the form of tetrafluoride anions allows the suppression of U by an order of magnitude relative to Np.

Ultrasensitive Radionuclide Analysis in Water and Sediments for Environmental Radiological Assessment near the Decommissioning Garigliano Nuclear Power Plant (Italy)

We report a high sensitivity study of actinides content in water and sediment matrices performed for the first time along the Garigliano river, near the nuclear power plant currently undergoing decommissioning, and in the marine environment surrounding the river mouth up to a depth of 100 m. Ultrasensitive accelerator mass spectrometry measurements were carried out to estimate the absolute values of 236U, 238U, 239Pu, and 240Pu concentrations and 236U/238U, and 239Pu/240Pu ratios. The accuracy of the measurements and the spatial distribution of the radionuclides enable us to discriminate the anthropogenic from the natural radionuclide’s contribution to the environmental radioactivity. The results indicate that the contribution to the anthropogenic contamination of past power plant operations is, in most of the examined environmental compartments, negligible compared to fallout. High resolution γ-ray spectrometry measurements for 137Cs and 40K show interesting correlations with the actinides results.

Accelerator mass spectrometry measurements of 93Zr for astrophysical and nuclear technology applications

Zirconium-93 is a long-lived radionuclide with a half-life of (1.61 ± 0.05) × 106 yr. Production cross sections for 93Zr by neutron capture on stable 92Zr in the keV and thermal energy ranges are important input parameters for astrophysical network calculations and nuclear industry, respectively. Despite their importance, existing experimental data suffer from large uncertainties. Here, the combination of neutron activation and accelerator mass spectrometry (AMS) is presented as an alternative method to online time-of-flight measurements for the determination of these cross sections. The main challenges for AMS of 93Zr are the interference from the stable isobar 93Nb and the production of suitable reference material. At the Heavy Ion Accelerator Facility (HIAF) the first challenge is tackled with the available high particle energies and by investigating different Zr compounds and extracted molecular beams. Using ZrF5− beams extracted from ZrF4 sample material, it is shown that the Nb background can be reduced by up to two orders of magnitude relative to the extraction of ZrO− beams from ZrO2. Using the 13+ charge state and particle energies of ∼190 MeV, 93Zr/Zr background levels in the 10−12 range are regularly achieved at HIAF. The ZrF5− output from ZrF4 samples may be highly variable but can be stabilised using an intimate mixture of ZrF4 and PbF2 at a ratio of 1:10 that has been dried down from a concentrated hydrofluoric acid solution. An option to produce a well-characterised 93Zr reference material by utilising the well-known 235U-fission yield of 93Zr is discussed. Once this remaining challenge is resolved, accurate measurements of the astrophysically and technologically relevant neutron-capture cross sections of 92Zr using AMS will be possible at HIAF.

Ultra-Sensitive Determination of Particulate, Gaseous Inorganic and Organic Iodine-129 and Iodine-127 in Ambient Air.

Atmospheric iodine cycling is of significance in climate change and environmental and health impacts. To better explore speciation transformation of atmospheric stable and radioactive iodine, an ultra-sensitive analytical method was established for determination of 129I and 127I in particulate, gaseous inorganic, and gaseous organic species, which was conducted with a self-designed cascade sampling apparatus, followed by their separation with a pyrolysis system and accelerator mass spectrometry and ICP-MS measurements. Combustion protocols for three sampling matrices and NaOH concentration for iodine trapping were optimized to achieve a safe analytical procedure with a high chemical yield of iodine. Based on the lowest concentrations of 129I and 127I, a suitable activated carbon product for adsorption of gaseous organic iodine was carefully selected. The detection limits of the three species were 0.30-2.21 ng m-3 for 127I and 0.05-0.22 × 105 atoms m-3 for 129I. This newly established method was successfully applied to analyze the levels and species of 129I and 127I in ambinet air from Xi'an, China, from May to August, 2020. Gaseous organic iodine was found to be the dominant species of 127I and 129I, accounting for about half of total iodine, and gaseous inorganic iodine and particulate iodine accounted for one-quarter each during the whole sampling period. Speciation variation of 129I and 127I indicates that speciation transformation apparently occurred at the turn of spring and summer, mainly between particulate and gaseous organic iodine. This study has implications on delicate tracing of the atmospheric behavior of iodine with long-lived anthropogenic 129I.

From lakes to ratios: 14C measurement process of the Finnish tree-ring research consortium

Annual and sub-annual tree-ring 14C measurements allow the study of past natural phenomena such as rapid 14C increases and solar behavior. In addition, they provide precise calibration data sets that help in improving the dating accuracy of past natural and cultural events. However, for the data to be comparable, it is important that laboratories describe the whole process from sample retrieval to eventual results. In this paper, we describe the full 14C measurement procedure adopted in the Finnish tree-ring consortium, including sample collection and preparation, dendrochronology, chemical pretreatment, combustion and graphitization, Accelerator Mass Spectrometry (AMS) measurements and data processing. In addition, we report the 14C background components for our traditional Closed-Tube Combustion (CTC) and Elemental Analyzer (EA) based processes, both yielding to high-quality data. Furthermore, we study the mass-dependence effects of tree-ring measurements and find them to be practically insignificant for ages up to several millennia but growing in significance when approaching the 14C limit.

R-Process Radioisotopes from Near-Earth Supernovae and Kilonovae

Abstract The astrophysical sites where r-process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter r-process species. The discovery of 60Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, 244Pu has now been detected, mostly overlapping with 60Fe pulses. However, the 244Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for r-process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of 244Pu and searches for other live isotopes could probe the origins of the r-process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live r-process radioisotopes produced in SNe and KNe that we present here. Given the presence of 244Pu, other r-process species such as 93Zr, 107Pd, 129I, 135Cs, 182Hf, 236U, 237Np, and 247Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS 129I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario.

VOLUMES OF WORTH—DELIMITING THE SAMPLE SIZE FOR RADIOCARBON DATING OF PARCHMENT

ABSTRACTMedieval manuscripts are invaluable archives of the written history of our past. Manuscripts can be dated and localized paleographically, but this method has its limitations. The Fragmenta membranea manuscript collection at the National Library of Finland has proved difficult to date using paleographic methods. Radiocarbon dating has been applied to manuscripts of parchment before, but a systematic protocol for radiocarbon dating of parchment has not been established with a minimally destructive sampling strategy. In this work, we have established a radiocarbon dating procedure for parchments combining a clean-room based chemical pretreatment process, elemental analyzer combustion, automatic graphitization and accelerator mass spectrometry (AMS) measurements to reduce the AMS target size from a typical 1 mg of carbon. Prolonged acid treatment resulted in improved dating accuracy, since this is consistent with the manufacturing process of medieval parchment involving a lime bath. Two different combustion processes were compared. The traditional closed tube combustion (CTC) method provided a well-established though labor-intensive way to produce 1 mg AMS targets. The Elemental Analyzer-based process (EA-HASE, Elemental Analyzer Helsinki Adaptive Sample prEparation line), is designed for fast combustion and smaller sample sizes. The EA-HASE process was capable of reproducing the simulated radiocarbon ages of known-age samples with AMS graphite target sizes of 0.3 mg of carbon, corresponding to a 3 mm2 area of a typical medieval parchment. The full potential of the process to go down to as little as 50 μg will be further explored in the future in parallel to studies of sample-specific contamination issues.

RADIOCARBON DATING AND DIET: THE JIAOJIA SITE IN CHINA

ABSTRACTThe Jiaojia site is the earliest city in the Haidai area of China, about 5000 years old. To obtain more accurately the beginning and end of this site, radiocarbon accelerator mass spectrometry (14C AMS) measurements, along with stable carbon and nitrogen isotope data, were collected from 13 bone samples. According to the measured dates, human diet was dominated by C4-based plants, and the Jiaojia site appeared before 2900 BC.

Radiocarbon Production Events and their Potential Relationship with the Schwabe Cycle

Extreme cosmic radiation events occurred in the years 774/5 and 993/4 CE, as revealed by anomalies in the concentration of radiocarbon in known-age tree-rings. Most hypotheses point towards intense solar storms as the cause for these events, although little direct experimental support for this claim has thus far come to light. In this study, we perform very high-precision accelerator mass spectrometry (AMS) measurements on dendrochronological tree-rings spanning the years of the events of interest, as well as the Carrington Event of 1859 CE, which is recognized as an extreme solar storm even though it did not generate an anomalous radiocarbon signature. Our data, comprising 169 new and previously published measurements, appear to delineate the modulation of radiocarbon production due to the Schwabe (11-year) solar cycle. Moreover, they suggest that all three events occurred around the maximum of the solar cycle, adding experimental support for a common solar origin.

The Bucharest 1 MV HVEE Accelerator Mass Spectrometer extended for measurements of hydrogen isotopes

The High Voltage Engineering Europa B.V. (HVEE) 1 MV spectrometer at NIPNE-Bucharest was extended to allow highly sensitive Accelerator Mass Spectrometry (AMS) measurements of tritium (3H). The new established analyzing procedure and a complete AMS experiment with tritium are described in detail.

Radiocarbon Dating Cremated Bone: A Case Study Comparing Laboratory Methods

ABSTRACTRadiocarbon (14C) results on cremated bone are frequently published in high-ranking journals, but 14C laboratories employ different pretreatment methods as they have divergent perceptions of what sources of contaminants might be present. We found pretreatment protocols to vary significantly between three laboratories (Brussels [RICH], Kiel [KIA], and Groningen [CIO]), which all have a long history of dating cremated bone. We present a case study of 6 sets of replicate dates, to compare laboratory pretreatment protocols, and a further 16 sets of inter-laboratory replicate measurements, which compare specific steps of the conversion and measuring process. The 14C results showed dates to be reproducible between the laboratories and consistent with the expected archaeological chronology. We found that differences in pretreatment, conversion to CO2 and accelerator mass spectrometry (AMS) measurement to have no measurable influence on the majority of obtained results, suggesting that any possible diagenesis was probably restricted to the most soluble ≤5% of each sample, as this proportion of the sample mass was removed under all laboratory protocols.

Monitoring the biogenic fraction of sugarcane-based plastic bags

For environmental reasons, the production of plastic from renewable sources is gaining importance worldwide. In the case of polyethylene made from sugarcane-based ethanol, Brazil, being the world leader in sugarcane production, plays a fundamental role. Nevertheless, the absence of national regulations for monitoring the manufacturing process or verifying the biogenic fraction of what is already on the market raises concerns in Brazil. The main reason for the lack of such regulations is that the only approach fully capable of distinguishing identical chemical compounds of biogenic or fossil origin is the measurement of radiocarbon concentrations using an expensive and time-consuming method. Nevertheless, the measurement of stable carbon isotopes ratios has proven to be an acceptable approach to distinguish between C4 plant-derived plastics and petroleum-derived plastics. The present study compares the potential of the conventional mass spectrometry and radiocarbon accelerator mass spectrometry techniques as tools to determine the biogenic fraction of green polyethylene in Brazil. For plastics derived from either corn or sugarcane sources, δ13C values less negative than −20‰ indicate biofractions of 51% or higher. Other values would indicate the need to follow up to the radiocarbon accelerator mass spectrometry measurement, since it would not be possible to distinguish between lower biofractions and the presence of wheat or soy. The conventional mass spectrometry method can be employed for the preliminary screening of bio-based materials in manufacturing industries, representing a relatively cheap and accessible way of inspecting these products in developing countries.

Assessing the dead carbon proportion of a modern speleothem from central Brazil

Abstract Geographic and temporal variations in atmospheric carbon isotopic ratios are recorded in environmental proxies. In temperate regions, this may assist in the construction of datasets for the calibration of radiocarbon ages. Over the tropics, the high growth rate of speleothems combined with high precision 230Th dating provides potential records for atmospheric 14C reconstruction. In this preliminary work, we investigate the isotopic composition (δ18O and δ13C) of a speleothem from central Brazil, precisely dated by the multi-collector inductively coupled plasma mass spectrometry technique (MC-ICP-MS). Radiocarbon Accelerator Mass Spectrometry (AMS) measurements were compared to the 14C concentration in the atmosphere during the nuclear tests period based on the Bomb13SH1-2 curve. Our results show that the speleothem dead carbon proportion is less than 20% between 1932 and 1992 AD while δ13C values vary between −14 and −9‰. Given that the empirical radiocarbon calibration curves for the Southern Hemisphere were constructed based on limited records, we discuss the potential and limitations of Brazilian speleothems for the evaluation of atmospheric 14C concentrations over the last millennia.

Accelerator mass spectrometry measurement of the reaction Cl35(n,γ)Cl36 at keV energies

Accelerator mass spectrometry measurement of the reaction <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>Cl</mml:mi><mml:mprescripts /><mml:none /><mml:mn>35</mml:mn></mml:mmultiscripts><mml:mo>(</mml:mo><mml:mi>n</mml:mi><mml:mo>,</mml:mo><mml:mi>γ</mml:mi><mml:mo>)</mml:mo><mml:mmultiscripts><mml:mi>Cl</mml:mi><mml:mprescripts /><mml:none /><mml:mn>36</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> at keV energies