MV Accelerator Mass Spectrometry Research Articles

Reaching environmental levels of 244Pu by accelerator mass spectrometry at the Centro Nacional de Aceleradores

244Pu (T1/2 = 81 My) is the longest-lived, most minor, and the most understudied Pu isotope. The anthropogenic production of 244Pu is linked to nuclear detonations. Reported 244Pu/239Pu atom ratios in environmental samples range from below 10−6 to above 10−3. This work discusses the performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain) to analyse 244Pu at environmental levels. The presence of 232Th traces in the Pu sample limits the sensitivity of the technique through the formation of the diatomic trication (232Th12C)3+, of mass 244 u, which must be suppressed by adjusting the stripper gas pressure. A244Pu background of 0.0075 fg (2 × 104 at) is demonstrated for samples that have undergone a chemical treatment. The reliability of the technique is proved through the analysis of three reference sediments provided by the International Atomic Energy Agency (IAEA-412, IAEA-465, IAEA-385). 244Pu results are complemented with 239Pu, 240Pu, 241Pu and 236U and their relative isotopic abundances are discussed.

Optimization of 10Be measurements at the 6 MV AMS facility DREAMS

We investigated benefits from raising the ion beam energy during measurements of 10Be with Accelerator Mass Spectrometry (AMS) at the 6MV DREAMS (DREsden AMS) facility. Increasing the terminal voltage to ≥5MV hardly reduces the yield of the Be2+ charge state after the accelerator if one applies only a thin Ar gas stripper and makes use of an overpopulation of the 2+ charge state with respect to the expected equilibrium charge state yield. As a further stripping to the 4+ charge state is conducted in a degrader foil after the analysing magnet, it is desirable to hit the foil with the highest available velocity in order to have optimal stripping of Be2+ to the fully stripped ion. At DREAMS the 10Be yield can be improved by a factor of 1.36. Applying a terminal voltage of 5.8MV the transport efficiency of 10Be from the ion source to the detector is ca. 32.5%.

Performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores for the analysis of 233U at environmental levels

233U (T1/2 = 0.159 My) has aroused much interest in the last few years because of the potential of 233U/236U to inform about anthropogenic U sources. The reported 233U/238U atom ratios in general environmental samples are in the 10−12–10−6 range. We demonstrate that 233U/238U abundance sensitivities at the 5 × 10−11 level can be achieved at the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain). Unresolved 234U, 235U and 232Th molecular fragments are identified as the main233U background contributors and procedures to subtract them are proposed. 233U/238U and 236U/238U atom ratios were analysed in the IAEA reference materials coded Soil-6, 300, 385, 410, and 412 at the CNA and at the 600 kV ETH AMS system for intercomparison. 233U/238U atom ratios for samples 412 and 385 were only reported by the ETH.

Characterization of the isobar separator for anions integrated into the A. E. Lalonde laboratory’s 3 MV AMS system

Accelerator Mass Spectrometry (AMS) of isotopes with abundant negative ion-forming isobars often requires the use of large accelerators to achieve high sensitivity measurements. The Isobar Separator for Anions (ISA) is a radio frequency quadrupole (RFQ) reaction cell system that can provide selective isobar suppression in the low energy system, prior to injection into an accelerator. A commercial version from Isobarex Corp. has been installed in a second injection line of the 3 MV tandem accelerator system at the A. E. Lalonde AMS Laboratory, University of Ottawa. Here, we present the characterization of the ISA for its optimization of S– suppression and Cl– transmission. He gas was selected as a cooling buffer gas, as it provided the best Cl– transmission of ∼50 % through the ISA column. These tests use NO2 as a reaction gas due to its well-known exothermic reaction with S– but endothermic reaction with Cl–. More than six orders of magnitude reduction of S to Cl has been observed.

Accumulation of ferromanganese crusts derived from carrier-free 10Be/9Be

The occurrence of 10Be in natural archives is commonly used to date their formation and growth on time scales of million years. Accelerator Mass Spectrometry (AMS) can perform a direct measurement of the 10Be/9Be ratio. The carrier-free method, in which no 9Be carrier is added to the original sample, is especially suitable for 10Be/9Be ratio determination in the marine environment. By normalizing the 10Be content to 9Be, temporal variations of Be uptake processes into the archive are eliminated.Here, we present a simple method for the chemical extraction of beryllium from ferromanganese (FeMn) crusts or nodules, the measurement procedure, and the first carrier-free 10Be/9Be measurements at the 3 MV AMS facility VERA. Several tests of chemical methods are discussed including different options to short-cut and accelerate the procedure for special cases. Results from FeMn crust 237KD from cruise VA13/2 in the Pacific ocean show the known 10Be/9Be distribution with depth that is commonly related to a changing growth rate of the archive. In this context we discuss the potential influence of diffusion and adsorption processes on the age models of FeMn crusts that are based on radioactive nuclides such as 10Be and 230Th. Including an open-system behavior for these isotopes in the description of their profiles allows interpreting the accumulation of crusts with a constant growth rate over millions of years and does not require the assumption of abrupt growth changes.

Method developments for accelerator mass spectrometry at CologneAMS, 53Mn/3He burial dating and ultra-small 14CO2 samples

Abstract Accelerator mass spectrometry (AMS) has a great potential for various geological applications. The precision and sensitivity is directly linked to technical developments. Therefore CologneAMS, the center for accelerator mass spectrometry of the University of Cologne ( Dewald et al., 2013a , Dewald et al., 2013b ), does extensive work on method developments for isotopic ratio measurement, for new applications and to improve the precision. We present two important technical developments: (1) dating of sediments with 53Mn and (2) ultra-small 14CO2 samples. (1) The age determination of discontinuously deposited sediments by measurement of cosmogenic 53Mn and 3He concentration in iron‑titaniumoxides (hematite, magnetite, titanomagnetite, ilmenite), where the measurement of the medium mass isotope 53Mn is difficult because of the interfering isobar 53Cr. It can be measured at only 2 laboratories worldwide. The new AMS system at the Cologne 10 MV FN tandem accelerator is therefore designed especially for the measurement of medium mass isotopes, e.g. 53Mn. It provides the opportunity to use several detector systems in different combinations: degrader foils with an electrostatic analyzer, a 4 m time-of-flight system, a new 135∘ gas-filled magnet, different gas ionization detectors and a projectile x-ray detector. With the implementation of the new 135∘ gas-filled magnet to the 10 MV FN-Tandem accelerator AMS beamline the first tests have shown an increase in transmission and reduction of blank value in comparrison to the measurement with the degrader foil technique (Schiffer et al. 2018). The background level was reduced by a factor of 3.3 and the error normalized sensitivity (Schiffer et al. 2018) was increased by a factor of 1.6. (2) For the measurement of extremely low carbon from cosmogenic in-situ produced 14C or from 14C content of bulk sediments, with 0.01% carbon, technical developments are required to measure low concentrations in terrestrial rocks of 100,000 atoms g−1 in quartz and to trace organic compounds with 10–50 μg of 14CO2 samples. It turned out, that the measurement of 14CO2 micro-samples with the gas-ion source of the Cologne 6 MV AMS system in combination with a gas-handling system is an alternative to the development of a micro-scale graphitization. Modern 1 μg CO2 samples, (14C/12C) = 1.18×10−12, can be measured with this system with a precision of 2.8%. The overall efficiency is 4%–6% and the reproducibility of standard samples is 0.9% with a blank level of 3–6×10−15.

Accelerator Mass Spectrometry of 237Np, 239Pu and 240Pu for environmental studies at the Centro Nacional de Aceleradores

Low-energy Accelerator Mass Spectrometry (AMS) systems (i.e. working with 1 MV terminal voltages and below) have demonstrated in the past their capability for the ultra-trace analyses of 236U and 239,240Pu in different field studies. The situation for 237Np has been different, mostly due to the constraints imposed by the lack of a Np isotopic tracer. Here, it is presented a comprehensive study on the performance of the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) for: i) the determination of 237Np using 242Pu as the AMS normalisation isotope and, ii) the efficient analysis of 239Pu, 240Pu and 237Np when they coexist in the same cathode with traces of natural uranium. Working procedures to analyse 237Np and 239Pu on one hand, and 240Pu on the other, are developed in order to meet competitive 238U suppression factors and counting efficiencies for every radionuclide. It is demonstrated that the sputtering-process-based temporal trend in the 237Np/242Pu AMS ratios show a coherent behaviour between the different studied matrixes, demonstrating the reliability of the necessary standard correction procedure in AMS. It is proved that 237Np and 239Pu concentrations at the 1 fg level and 240Pu concentrations at the 0.1 fg level can be quantified in samples containing 238U traces. The technique is applied to the 239,240Pu and 237Np analysis of a seawater reference sample supplied by the International Atomic Energy Agency (IAEA): IAEA-443.

Meteoric 10Be in aerosol filters in the city of Seville

Cosmogenic radionuclides in the one-million-year half-life range, like 10Be, find application fields in several Sciences. They are powerful tools in Geology and Geochronology, as they are very important tracers on the Earth, being utilized as chronometer. Meteoric 10Be (T1/2 = 1.39 × 106 y) associated to aerosols can be used as a tracer of atmospheric processes and specifically as indicators of the cosmogenic interactions in lower Stratosphere, upper Troposphere, the air exchange between both and deposition processes on the Earth surface. The applications of 10Be are even more relevant when combined with other radionuclides such as 26Al. In order to provide new data about concentration 10Be in this type of samples, the first atmospheric air filters in Spain have been analysed. Values around 104 at/m3 (atoms per cubic meter of air) for 10Be have been obtained. Due to the location and the features of the sampling site (urban area, at sea level and mid latitude), a new radiochemical procedure was designed and developed in our laboratory for the Accelerator Mass Spectrometry (AMS) measurement of 10Be in this kind of samples. The samples were measured in SARA, the 1 MV AMS system at Centro Nacional de Aceleradores (CNA).

A New capability for 41Ca analysis using [formula omitted] at the Xi’an-AMS

The analysis of 41Ca can be quantified by measuring the ratio 41Ca/40Ca. At present, ratios of 41Ca/40Ca ≤ 10−11 can only be measured by accelerator mass spectrometry (AMS). The sensitivity is mainly limited by the interference of the isobar 41K. With compact AMS (≤1 MV), abundance sensitivities of 10−11 to 10−12 have been demonstrated, but this may necessitate the measurement of 39K to correct for the 41K background. With a 3 MV AMS, the dE/dx method can still be used to partially separate 41Ca from 41K. In this work, a new capability for 41Ca analysis has been tested at the Xi’an-AMS. Ca4+ was chosen to achieve a balanced performance between 41Ca/41K separation and transmission efficiency. A 41Ca/40Ca background level of near 10−13 was achieved without the need for 39K correction. This new analytical capability at our facility was then applied to 41Ca tracer samples from our studies on the “White Jade” land snail shells, in which 41Ca was used as a tracer for studying the absorption rate of calcium.

Recent developments of the 1 MV AMS facility at the Centro Nacional de Aceleradores

The Centro Nacional de Aceleradores (CNA) hosts a 1MV accelerator mass spectrometry (AMS) apparatus since September 2005. In order to improve its overall performance, several updates have been made on the existing facility during the last 10years of operation. In this paper, two modifications conducted in 2015 will be described.To increase the transmission of the ions through the accelerator, the stripping gas on the 1MV CNA machine was changed from Ar to He. The measured maximum transmission for almost every isotope results to be higher, especially for heavy masses: for instance, in the case of uranium in the 3+ charge state, the transmission increased from 11% with Ar gas to about 38% with He gas.The second advance consisted of the substitution of the existing gas ionization chamber with a new one provided by ETH Zurich. The ETH detector features with its miniaturized design and is optimized for low energy AMS (i.e. very low electronic noise and efficient charge collection). As the electronic noise is the most important contribution to the resolution for light ions, the total energy resolution has been reduced by 15% in the case of 10Be, allowing a better discrimination against its isobar, 10B. For the heaviest radionuclides where the quality of the spectra is determined by the charge carrier production in the gas, the resolution for 2.7MeV uranium ions was improved by 30%, probably due to a more efficient charge collection.

Low energy AMS of americium and curium

Accelerator mass spectrometry (AMS) has evolved over the past years as one of the most sensitive, selective, and robust techniques for actinide analyses. While analyses of U and Pu isotopes have already become routine at the ETH Zurich 0.5MV AMS system “Tandy”, there is an increasing demand for highly sensitive analyses of the higher actinides such as Am and Cm for bioassay applications and beyond. In order to extend the actinide capabilities of the compact ETH Zurich AMS system and to develop new, more sensitive bioassay routines, a pilot study was carried out. The aim was to investigate and document the performance and the potential background of Am and Cm analyses with low energy AMS. Our results show that 241Am and Cm isotopes can be determined relative to a 243Am tracer if samples and AMS standards are prepared identically with regard to the matrix elements, in which the sample is dispersed. In this first test, detection limits for Cm and Am isotopes are all in the sub-femtogram range and even below 100ag for Cm isotopes. In a systematic background study in the mass range of the Cm isotopes, two formerly unknown metastable triply charged Th molecules were found on amu(244) and amu(248). The presence of such a background is not a principal problem for AMS if the stripper pressure is increased accordingly. Based on our first results, we conclude that ultra-trace analyses of Am and Cm isotopes for bioassay are very well possible with low energy AMS.

A new HVE 6 MV AMS system at the University of Cologne

CologneAMS is the new Centre for Accelerator Mass Spectrometry (AMS) at the University of Cologne. It will operate a dedicated AMS system designed to measure all standard cosmogenic nuclides ( 10Be, 14C, 26Al, 36Cl, 41Ca, 129I) and which uses a 6 MV Tandetron™ accelerator equipped with an all solid-state power supply, foil and gas stripper. The system also enables a sensitive detection of heavy ions up to 239U and 244Pu. The high-energy mass-spectrometer consists of a 90 degree magnet with a radius of 2 m and a mass-energy product of 351 AMU MeV to allow the detection of 244Pu 5+ up to the maximum terminal voltage of 6 MV. This magnet is followed by an electrostatic energy analyzer and a switching magnet that can transport the rare isotope beam into various beamlines. The switching magnet forms a third analyzing element which is needed especially for the sensitive detection of heavy elements. So far two beamlines are equipped with their own detection system. One of these lines is used for suppression of isobaric background in the case of the analysis of e.g. 36Cl. This is accomplished by an absorber foil which generates a Z-dependent energy loss in combination with a momentum/charge-state selection via a 120 degree magnet that features up to 30 mrad acceptance for efficient beam transport. In this contribution we will introduce the new Centre, the layout and specific characteristics of the AMS system as well as the main topics of the future scientific work to be performed at CologneAMS.

The Low-Energy Isobar Separator for Anions: Progress Report

The suppression of interferences from atomic and molecular isobars is a key requirement for the extension of accelerator mass spectrometry (AMS) to the analysis of new cosmogenic isotopes and for increasing the range of applications for small AMS systems. In earlier work, it was shown that unwanted isobars can be eliminated by anion-gas reactions (Litherland et al. 2007). Recently, a prototype system in which such reactions could be applied to ions from an AMS ion source, the Isobar Separator for Anions (ISA), was described (Eliades et al. 2009). This system decelerates the beam of rare anions from keV to eV energies, guides them through a single radiofrequency quadrupole (RFQ) gas cell, and re-accelerates them for further analysis in a 2.5MV AMS system. Tests of this system with Cl and S anions and NO2 gas showed a suppression of S with respect to Cl of over 6 orders of magnitude, with a transmission of ∼30% for the Cl beam. In this work, results of the analysis of a range of standard reference materials are reported; these show the linearity of the system for measuring the 36Cl/35Cl ratio over a span of 2 orders of magnitude. Further tests, using the AMS system as a diagnostic tool, have provided clues about the loss of Cl at higher cell pressure and the nature of the residual low level of S transmission. These lead to the assessment of various gases for cooling the Cl– beam. Suppression measurements for 41K in the analysis of 41Ca, using NO2 as a reaction gas, are also discussed. These preliminary measurements have provided data for the development of a more advanced system with separate cooling and reaction cells.

A highly sensitive method for the reassessment and quantification of 239Pu in urine samples based on a 1 MV accelerator mass spectrometry system

A new and highly sensitive method for the determination of 239Pu in human urine has been developed permitting the reassessment of planchets initially prepared for alpha spectrometry (AS) analysis in the context of internal dosimetry. A set of urine samples (volume: 500 mL) was spiked with known quantities of 239Pu, ranging from 2 to 120 fg (4.6 μBq–0.3 mBq), employing 14 pg (2.05 mBq) of 242Pu as internal standard. The Pu was purified by ion-chromatography using BioRad AG1X2 anion-exchange resins (Bio-Rad Laboratories Inc.). The chemical yield was determined by alpha-spectrometry, being about 80%. Afterwards, the planchets so obtained were leached with diluted HNO3 and the dissolved plutonium was determined by Accelerator Mass Spectrometry (AMS) at the Centro Nacional de Aceleradores (CNA) in Seville, Spain. The minimum detectable activity (MDA) for the AMS measurements was determined through the study of a set of procedural blanks, giving figures of about 0.44 fg (∼1 μBq) per sample. This contrasts with the MDA obtained by AS for the same set of samples, of about 50 fg (∼0.1 mBq). The results now presented helps to demonstrate that the routine measurement of 239Pu at ultra trace levels in human urine samples is possible with the new-generation of compact AMS systems, offering a highly sensitive method for the reassessing of planchets prepared for bioassay purposes.

The LLNL accelerator mass spectrometry system for biochemical 14C-measurements

We report on recent improvements made to our 1 MV accelerator mass spectrometry system that is dedicated to 14C quantification of biochemical samples. Increased vacuum pumping capacity near the high voltage terminal has resulted in a two-fold reduction of system backgrounds to 0.04 amol 14C/mg carbon. Carbon ion transmission through the accelerator has also improved a few percent. We have also developed tritium measurement capability on this spectrometer. The 3H/1H isotopic ratio of a milligram-sized processed tap water sample has been measured at 4±1×10−16 (430±110 μBq/mg H). Measurement throughput for a typical biochemical 3H sample is estimated to be ∼10 min/sample.

The LLNL accelerator mass spectrometry system for biochemical 14C-measurements

We report on recent improvements made to our 1 MV accelerator mass spectrometry system that is dedicated to 14 C quantification of biochemical samples. Increased vacuum pumping capacity near the high voltage terminal has resulted in a two-fold reduction of system backgrounds to 0.04 amol 14 C/mg carbon. Carbon ion transmission through the accelerator has also improved a few percent. We have also developed tritium measurement capability on this spectrometer. The 3 H/ 1 H isotopic ratio of a milligram-sized processed tap water sample has been measured at 4 ± 1 × 10 −16 (430 ± 110 μBq/mg H). Measurement throughput for a typical biochemical 3 H sample is estimated to be ∼10 min/sample.

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.