Isobaric identification techniques of AMS at CIAE

Some long-lived nuclides, such as ³⁶Cl, ⁴¹Ca, ⁵³Mn, ⁷⁹Se, etc., are very interested in life science, environment science, geo- and cosmo-sciences, nuclear wastes management, and other fields. Taking the advantages in high sensitivity and the strong ability to reduce the interferences from molecular ions and isobars, AMS has been one of the most promising methods for the measurement of these nuclides. However, the sensitivity of AMS is often unsatisfactory due to the interferences of stable isobars especially for medium and heavy radioisotopes. Gas-filled time of flight (GF-TOF), Gas-filled Magnet with a time of flight (GFM-TOF), Bragg Curve detector and energy loss (ΔE) combined with a Q3D magnetic spectrometer (ΔE-Q3D) are among the techniques used or being developed in AMS lab of China Institute of Atomic Energy, in an attempt to further reduce the interferences from isobars. These techniques will be tested in our AMS measurement of ⁵³Mn, ⁷⁹Se, ⁹³Zr, ⁹⁹Tc, etc., for identifying isobaric interferences.     

Development of a fraction collector for coupling gas chromatography with an AMS facility

It has been shown that microscale ¹⁴C measurements are possible by using a gas handling system and a gas ion source [T. Uhl, W. Kretschmer, W. Luppold, A. Scharf, AMS measurements from microgram to milligram, Nucl. Instr. and Meth. (2005) 474 (240th ed.), T. Uhl, W. Luppold, A. Rottenbach, A. Scharf, K. Kritzler, W. Kretschmer, Development of an automatic gas handling system for microscale AMS (¹⁴C) measurements, Nucl. Instr. and Meth. (2007) 303 (259th ed.)]. In Erlangen a gas handling system was especially developed for environmental and biomedical investigations. For the separation of the compound of interest a standard gas chromatograph (GC) is used. To minimize the sample contamination and sample loss we have designed a fraction collector that connects a GC and an elemental analyzer (EA) directly. The selected compound is combusted in the EA and the resulting CO₂ is then transferred into the gas handling system for AMS measurements. From the beginning of GC preparation up to the AMS measurement the sample is in a closed line. All operations are fully automated, so no manual operations are necessary. This guarantees high cleanness and maximum sample yield. Preliminary measurements are done using modern and old ethyl alcohol (from fermentation and of petrochemical origin, respectively). The results are consistent with their expected values although cross contamination and background signal increased as the sample mass was decreased.     

Analysis and application of heavy isotopes in the environment

A growing number of AMS laboratories are pursuing applications of actinides. We discuss the basic requirements of the AMS technique of heavy (i.e., above ～150 amu) isotopes, present the setup at the Vienna Environmental Research Accelerator (VERA) which is especially well suited for the isotope ²³⁶U, and give a comparison with other AMS facilities. Special emphasis will be put on elaborating the effective detection limits for environmental samples with respect to other mass spectrometric methods.At VERA, we have carried out measurements for radiation protection and environmental monitoring (²³⁶U, ^{239,240,241,242,244}Pu), astrophysics (¹⁸²Hf, ²³⁶U, ²⁴⁴Pu, ²⁴⁷Cm), nuclear physics, and a search for long-lived super-heavy elements (Z > 100). We are pursuing the environmental distribution of ²³⁶U, as a basis for geological applications of natural ²³⁶U.     

Isobar separation at very low energy for AMS

The separation of atomic and molecular isobars, prior to injection into a tandem accelerator for Accelerator Mass Spectrometry (AMS), is discussed. To accomplish this separation, the anions from a standard sputter ion source are retarded to eV energy. The advantages of using very low energy (eV) for this purpose are twofold. The ionic reactions in gases can be isobar specific and the multiple scattering of the eV ions, unlike that at higher energy, can be controlled in linear radio-frequency multipoles. An example of current interest to AMS practice, the suppression of the S⁻ isobar ions from negative ion sources generating mainly Cl⁻ ions, will be described. It will be argued that this is a universal method for isobar separation prior to AMS, which is applicable to atomic anions and cations as well as their molecular counterparts. This procedure should be applicable to the AMS analysis of most rare radioactive species, as atomic or molecular ions, starting with either anions or cations, with appropriate charge changing. In some cases the ions may be analysable without AMS.     

Applications of a compact ionization chamber in AMS at energies below 1 MeV/amu

The increasing demand for measuring long-lived radionuclides with small AMS machines at energies below 1 MeV per nucleon raises the need for compact detectors which still have a decent energy resolution and allow for a clear identification of the incident particles. Based on a design by the AMS group at the ETH Zurich a compact gas ionization chamber was built and installed at the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator). The main challenge in AMS is the detection of rare isotope species in the presence of strong isotopic and isobaric interferences. The task of the ionization chamber is the suppression of the unwanted isobar by separating the ions via their different stopping powers. Measurements of ³⁶Cl at VERA showed an achieved suppression of the unwanted stable isobar ³⁶S of 3 × 10⁻⁴ and measurements of ¹⁰Be showed an achieved suppression of ¹⁰B of at least 3 × 10⁻⁶. Additional suppression of the isobaric ions can be achieved by a degrader foil technique applied to ¹⁰Be measurements by G.M. Raisbeck. In combination with the new ionization chamber the achieved suppression of ¹⁰B is at least 10⁻¹⁰. Measurements of blank samples at VERA show that the background for AMS with ¹⁰Be is below 2 × 10⁻¹⁵.     

High precision C AMS at CIRCE

The CIRCE AMS system started operation in March 2005. The measurement of isotopic ratios ¹⁴C/¹²C in samples of archaeological and environmental interest has rapidly attained high precision and accuracy levels in routine operation. The results of the intercomparison campaign in the framework of the VIRI program, as well as the outcome of a statistical analysis of the about 200 control measurements performed with standard samples, have shown the capability of the whole system for high precision measurements (δR/R < 0.3%), allowing systematic investigations in both archaeological and environmental sciences. ²⁶Al AMS has been implemented for the measurement of the astrophysically relevant ²⁵Mg(p,γ)²⁶Al reaction cross section, while a beam line is under construction for the measurement of actinides isotopic ratios.     

On the measurement of 10Be on the 1 MV compact AMS system at the Centro Nacional de Aceleradores (Spain)

In this work we present the most recent improvements performed by our group on ¹⁰Be measurements on the 1 MV AMS system recently set up at the CNA (Centro Nacional de Aceleradores), in Seville (Spain). Our efforts have been focused on the study of the viability of our system for BeO and BeF^? measurements. To achieve this, different standard materials have been measured to demonstrate the reliability of the system for BeO measurements in a wide ¹⁰Be/⁹Be atomic ratio range and several environmental samples have been studied both at the 1 MV AMS CNA facility and at the 6 MV AMS ETH-PSI facility of Zurich to validate our measurements. The results show a good agreement between laboratories. New experiments also have been carried out selecting 1+ and 2+ charge states at the exit of the accelerator and inserting Si₃N_3.1 foils with different thicknesses to separate ¹⁰Be from its isobar, ¹⁰B. The influence of each foil on the overall transmission (detected ¹⁰Be compared to BeO^? injected into the accelerator) and background level was also assessed. In addition some tests were also done to assess the viability of BeF₂ and BaBeF₄ measurements at our system. Several metal matrices and cathode preparation procedures for BeO samples were investigated to maximize current and cathode lifetime.     

New results on Xi’an-AMS and sample preparation systems at Xi’an-AMS center

The Institute of Earth Environment of the Chinese Academy of Sciences and Xi’an Jiaotong University have jointly created an AMS center based on a 3 MV multi-element accelerator mass spectrometer (AMS). The main focus of the Xi’an-AMS center will be earth environmental studies, archeology and biomedical research. This paper summarizes that the end-user recognized features of the Xi’an-AMS and reports new results obtained during the final acceptance tests for nuclides ¹⁰Be and ²⁶Al, for which the background for ratio ¹⁰Be/⁹Be of 3.65 × 10⁻¹⁵ was demonstrated and the ²⁶Al precision test with terminal 3 MV was performed. We also introduce the new built graphite and BeO sample preparation systems and the preparation procedures. We also discuss the recent measurements obtained using our new machine after the acceptance tests.     

Status and research programs of the multinuclide accelerator mass spectrometry system at the University of Tsukuba

We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12 MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of ¹⁴C, ²⁶Al, ³⁶Cl and ¹²⁹I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of ³⁶Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the ³⁶Cl/Cl ratio is lower than 1 × 10^?15 with a halite sample. We have measured over 500 samples in 1 year, including samples for earth and environmental sciences and nuclear safety research.     

重核离子束成分的加速器质谱分析

为拓展加速器质量技术测量范围及测量放射性核束成分,建立了利用入射离子发射特征Ｘ射线鉴别同量异位素的方法,开展了利用ＡＭＳ测量重核离子束成分的工作。     

10Be and 26Al measurements at the Zurich 6 MV Tandem AMS facility

The setups for the ¹⁰Be and ²⁶Al AMS measurements at the Zurich 6 MV EN Tandem AMS facility are presented and data analysis procedures for both radionuclides are discussed. Performance parameters of the system are shown. In-house AMS standards are compared to commercially available AMS standards.     

Nucleogenic Cl, U and Pu in uranium ores

The nucleogenic isotopes ³⁶Cl, ²³⁶U and ²³⁹Pu are produced naturally in subsurface environments via neutron capture of thermal and epithermal neutrons. Concentrations are, however, very low and accelerator mass spectrometry (AMS) is required for quantitative measurements. A particular challenge is presented by the measurement of ²³⁶U/²³⁸U ratios down to the level of 10⁻¹³ that is expected from rocks with low uranium concentration. Here, we present the AMS methodology that has been developed at the ANU for measuring ²³⁶U/²³⁸U ratios at this level. The more established methodologies for ³⁶Cl and ²³⁹Pu measurements are also summarised. These capabilities are then used to characterize the ³⁶Cl, ²³⁶U and ²³⁹Pu concentrations in a range of uranium ores. A simple model of the neutron production and capture processes in subsurface environments has been developed and is presented. It is shown that nucleogenic ³⁶Cl, ²³⁶U and ²³⁹Pu can be used to determine both thermal and epithermal neutron fluxes in subsurface environments. Potential applications include uranium exploration and monitoring of the environmental impact of uranium mining.     

The relevance of ion optics for the development of small AMS facilities

An ion optics program is presented, which addresses some of the specific problems of accelerator mass spectrometry (AMS). Ion beams having a phase space with angular distributions based on small angle scattering and with energy distributions caused by the straggling in foils or stripper gas can be included in transmission calculations. As an example, a new design for ¹⁰Be measurements with the 600 kV AMS system at ETH Zurich including a silicon nitride degrader foil is discussed, which will allow competitive measurements of this cosmogenic radionuclide at low energies. This system should also improve background suppression for other AMS nuclides.     

Protactinium-231: A new radionuclide for AMS

For the first time, an AMS system was used to determine concentrations of the actinide Protactinium-231. ²³¹Pa has widespread applications in the earth sciences. It can be used for U-series disequilibrium dating, and ²³¹Pa is an important tracer in Paleoceanography. The Pa isotopes were measured with the compact ETH/PSI-AMS facility TANDY operating at about 300 kV. The linearity of the AMS is documented with two standard-dilution experiments and first measurements of natural samples from very different climate archives are presented. Our results show that it is possible to determine ²³¹Pa amounts in the lower femtogram (1 fg = 10⁻¹⁵ g) range with the TANDY. In natural samples, ²³¹Pa concentrations between 1 and 4 pg/g (1 pg = 10⁻¹² g) were measured with an average total error of 3% (one sigma). The average over all reproducibility of these first measurements was better than 2% with clear potential for improvement.     

Towards more precise Be and Cl data from measurements at the 10 level: Influence of sample preparation

The spreading application of accelerator mass spectrometry (AMS) to the geosciences will require measurement of increasing numbers of samples with low ¹⁰Be/⁹Be and ³⁶Cl/Cl isotopic ratios. To distinguish radionuclide concentrations in samples from corresponding processing blanks, samples must be prepared using stable isotope carriers with low intrinsic radionuclide concentrations. Measurements at different AMS facilities have shown that commercially available ⁹Be carriers rarely meet these requirements and use of ⁹Be carriers prepared from Be-containing minerals such as Be₂SiO₄ is advisable. For precise determinations at the low 10⁻¹⁴ level, samples need to produce the highest ⁹Be currents possible. Measurements performed at the two AMS facilities in France show that mixing BeO with Nb powder generally yields higher ⁹Be currents than mixing with Ag powder. Contamination of BeO by other elements such as Ti or Al will reduce the current by a simple dilution effect, thus limiting the statistical precision with which ¹⁰Be can be determined. In the case of ³⁶Cl analyses, repeated water-leaching of calcite samples sufficiently removes all atmospheric ³⁶Cl contamination, allowing determination of terrestrial cosmogenic in situ produced ³⁶Cl concentrations for surface exposure dating.     

Plutonium measurements on the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA)

Plutonium isotopes have been recently added to the list of radionuclides that can be measured with the new generation of compact AMS facilities. In this paper we present first experimental results concerning the development of the plutonium AMS technique at 680 kV on the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) in Sevilla, Spain. This is the first compact AMS machine designed and manufactured by High Voltage Engineering Europa. As we demonstrate, the obtained backgrounds for ^239,240Pu, of about 10⁶ atoms, and the ²³⁹Pu/²³⁸U mass suppression factor, in the range of 10⁻⁹, compare to the ones achieved on other AMS facilities. With the measurement of reference materials provided by the International Atomic Energy Agency (IAEA-375, IAEA-Soil-6, IAEA-381) and samples already studied on the 600 kV compact ETH/PSI AMS system at Zürich, we show that the CNA system can be perfectly used for the routine measurement of plutonium isotopes at environmental levels.     

中国原子能科学研究院的PX-AMS系统及其应用(英文)

加速器质谱(AMS)中的入射离子X射线方法是为解决AMS测量中重核同量异位素而发展的一种方法(PX AMS),在中国原子能科学研究院建立了PX AMS方法之后,利用这套系统开展了79Se,75Se,64Cu等核素的PX AMS方法测量,基于此技术实现了79Se,75Se半衰期的测量和64Cu放射性核束强度及库仑激发截面的测量。     

The new sample preparation line for radiocarbon measurements on atmospheric aerosol at LABEC

Radiocarbon measurements on the carbonaceous aerosol fractions have been demonstrated as an effective tool for aerosol source apportionment. For these measurements, a new sample preparation facility was installed at the INFN-LABEC laboratory of Florence (Italy). The line was designed to allow the preparation of samples from different carbonaceous fractions: the combustion of the aerosol samples can be performed in helium or oxygen flows, according to thermal sequences. The evolved CO₂ is cryogenically trapped and reduced to graphite, which is the target material for following Accelerator Mass Spectrometry (AMS) ¹⁴C measurements. This preparation line is described in detail in the paper. As a first step, the line was tested by means of AMS measurements performed on standards to check the reproducibility and the accuracy of the system; moreover, preliminary measurements on the total carbon fraction in aerosol samples were made. Results of these measurements are also reported.     

Nuclear data sheets for A = 159

Nuclear data based upon reaction and radioactivity studies of mass 159 nuclei are presented.For A = 159 all nuclei with 63 ?Z?72 with the exception of Yb and Lu have been reported; but not much is known for Eu, Er, Tm, and Hf isobars other than their ground-state properties. The only stable nucleus with A = 159 is ¹⁵⁹Tb, and it has been studied in considerable detail both by nuclear reactions and radioactive decay of its neighboring isobars. Because of ambiguity in beta branching in ¹⁵⁹Eu decay and since the beta branch to ¹⁵⁹Tb g.s. in ¹⁵⁹Gd decay is known only approximately, the normalizations in these radioactive decays are rather uncertain.For brevity some of the older data have been omitted or referenced as other measurements.It has been attempted to include all available data prior to February 1, 1973.     

Competitive 10Be measurements below 1 MeV with the upgraded ETH–TANDY AMS facility

Competitive ¹⁰Be measurements at energies as low as 0.75 MeV are now possible with the compact ETH AMS system TANDY. In this paper we describe and discuss the modifications that led to the significantly improved performance for ¹⁰Be at the 0.6 MV accelerator. Results from the first routine measurement show that ¹⁰Be on the upgraded TANDY is now fully competitive with larger AMS systems with respect to background and measurement precision. The total efficiency for ¹⁰Be is comparable to our large 6 MV Tandem system and thus sufficient for the full range of applications in the Earth and Environmental Sciences.