[en] Accelerator Mass Spectrometry (AMS) adds the techniques of higher energy charged particle acceleration to the basic principles of Isotope Ratio Mass Spectrometry (IRMS) to provide extremely low detection capability (below 1 femtogram) of rare isotopes in samples of natural materials as small as 1 mg. Depending on the element selected and the configuration of the equipment, rare isotope sensitivities can reach less than one part in 10${}^{15}$. The advantages of this small sample size and high sensitivity for the detection of rare isotopes include a) the economic benefit of collecting, shipping and preparing much smaller samples, and b) the ability to analyse specific chemical compounds within the sample. For the latter advantage, the pathway taken by that compound through a complex system can be more precisely traced or, in the case of radioactive isotopes, more precise chronological information can be provided. The paper is an amplification of material which was presented at the IAEA International Conference on Accelerators for Research and Sustainable Development: novel concepts and technical innovation. It begins with a basic overview of AMS technology, with an emphasis on how the use of higher energy contributes to this enhanced sensitivity, and then provides several examples of new AMS technologies which reduce the energy and space requirements for such systems. Several examples of applications which contribute to the investigation of sustainability in other areas of environmental concern are then briefly described.

[en] Full text: The cesium-sputter negative-ion source is a fundamental component of accelerator mass spectrometry studies. Improvements in ion current and output emittance allow for higher precision measurements and potential for new applications. The High Voltage Engineering Europa SO-110C ion source has been modeled using Integrated Engineering Software’s Lorentz 2E ion trajectory simulation software. This software includes the mutual space charge interactions between the incoming cesium ions from their production in the ionizer and the outgoing negative ion beam from the target (cathode). Simulations examined the effects of changing the geometry of various source components, electrode potentials, ion currents, position of the target and negative ion mass. The simulations demonstrated that, as the cesium current is increased, the cesium beam broadens by its own space charge repulsion. This affects its focusing and distribution on the sample material. It is important that the cesium cover the outer proportions of the sample well for best usage of the material and stability of the outgoing negative ion beam. Changes in geometry and electrode potentials can mitigate this effect. Informed by these simulations, experiments at the A.E. Lalonde Accelerator Mass Spectrometry Laboratory (Lalonde) recessed the target in incremental 1 mm steps (targets were translated away from the ionizer along the axis of symmetry). Custom target bases were machined to facilitate these recesses without the need to modify the target pressing procedure. The abundant isotopes were measured using the post-accelerator offset Faraday Cups and rare isotopes at the gas ionization detector to compare outputs at various settings. These tests were first run at routine ¹⁴C measurement settings (6 kV target-ionizer potential difference, 115°C cesium oven temperature) on graphite blanks. At these settings, a target recess of 1 mm gave the most stable output with the highest usage of sample material. A second experiment, using targets made from a ¹⁰Be standard, expanded this study by increasing the cesium oven temperature (and hence cesium current) incrementally from 130-140°C, while also varying the target-ionizer potential difference (4-11 kV). This multi-dimensional study gave several promising settings, resulting in the most precise measurement of ¹⁰Be performed to date at Lalonde. A demonstration of key simulations and a comparison with experimental results will be presented.

[en] The development of Accelerator Mass Spectrometry (AMS) has led to remarkable advances in the ability to detect at very low isotopic ratio several radionuclides of great interest in many scientific fields. However, expanding the application range of AMS to new radionuclides may require the use of isobaric separation techniques different from those commonly used in conventional AMS. Separation techniques based on DE/dx separation in foils or gases, gas ionization detectors or gas-filled magnets in many cases require larger accelerators. These currently limit the extension of AMS to a wider variety of radionuclides, despite the quality and imagination of AMS scientists who routinely apply these techniques to separate isobars from ''classical'' radionuclides. To be successful, any new isobaric separation technique will need to be integrable into existing AMS systems without major modification of installed equipment and will also need to provide efficient transmission of the radionuclide of interest to preserve the current ability of AMS to measure, in reasonable time and on milligram samples, isotopic ratios inaccessible by other techniques. Other important features to consider will be the cost and reliability of the additional equipment to be installed, the relative lengthening of the AMS line that may be required and the flexibility of these new techniques to be quickly programmed by the user to handle a wide range of radionuclides, ideally without requiring modification to hardware.

[en] Full text: 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 radiofrequency quadrupole (RFQ) reaction cell system that provides selective isobar suppression of many of these isotopes in the low energy system, prior to injection into an accelerator. The ISA can then facilitate the measurement of these ions using smaller accelerators. A commercial version from Isobarex Corp. (Vaughan, Ontario, Canada) has been installed into a separate Research Line of the 3 MV tandem accelerator system at the A. E. Lalonde AMS Laboratory, University of Ottawa. The Research Line consists of a Cs+ Sputter Ion Source that produces a 20-35 keV anion beam, which is energy and mass analyzed before injection into the ISA. The ISA includes a DC deceleration region, a combined cooling and reaction cell, and a DC re-acceleration region. The deceleration region reduces the beam energy to a level at which the RFQ cell can capture and contain the ions. The cell is filled with an inert cooling gas that has been experimentally selected to further reduce the ion energy and therefore facilitate charge exchange or other chemical reactions between the interfering isobar and the reaction gas, as well as enabling the highest transmission of the isotope of interest. A reaction gas, chosen to preferentially react with the interfering isobar, is also contained within the cell. RFQ segments along the length of the cell create a potential well, which limits the divergence of the traversing ions. DC offset voltages on these RFQ segments maintain a controlled ion velocity through the cell. After exiting the cell, the wanted ions are reaccelerated prior to injection into the tandem accelerator for conventional AMS analysis. Here we present ISA characterization for best achieved sulfur suppression and chlorine transmission. These tests use NO₂ as the reaction gas due to its well-known exothermic reaction with sulfur anions but endothermic reaction with chlorine anions [1]. Helium was selected as the cooling buffer gas, as it provided the best chlorine transmission of ~50% through the ISA column. Over six orders of magnitude reduction of sulfur-36 to chlorine-37 has been observed. Using the sulfur suppression from the ISA and the degree of dE/dx separation for 12 MeV ions in the detector offered by the 3MV-AMS system, a chlorine-36/chlorine-37 abundance sensitivity of ~7x10-¹⁵ was achieved. The ISA will be used to measure chlorine-36 samples and its applications will soon be extended to additional isotopes involving, for example, the suppression of ⁹⁰ZrF₃- and ¹³⁵BaF₂-/¹³⁷ BaF₂- in the measurements of ⁹⁰SrF₃- and ¹³⁵CsF₂-/¹³⁷CsF₂-, respectively.

[en] The measurement of rare radioactive lead isotopes ("2"0"5Pb or "2"1"0Pb) by AMS requires the production of strong Pb negative molecular anion beams from the ion source. This paper summarizes the results of tests of different target composition on the strength and stability of "2"0"8PbF_3"− currents and "2"1"0Pb counts. In an 834 SIMS-type Cs"+ sputter source, the superhalogen, PbF_3"− had the largest current or ionization efficiency from a survey of Pb molecular anions. The target matrix that produced the largest current of PbF_3"− was composed of PbF_2, AgF_2 and CsF. The ratio of AgF_2 and CsF does not affect the ionization efficiency of PbF_3"−. Chemically refluxed targets of PbF_2, AgF_2 and CsF increased the ionization efficiency of PbF_3"−. The count rate of the rare isotope, "2"1"0Pb, was increased with the addition of microgram quantities of stable PbF_2 to the targets. In an SO-110 type Cs"+ sputter source the ionization efficiency of PbF_3"− was increased with lower rather than higher Cs"+ fluence.

[en] The long lived radioisotope "1"2"9I is a uranium fission product, and an environmental contaminant of the nuclear age. Consequently, it can trace anthropogenic releases of "1"2"9I in watersheds, and has been identified as a potential means to distinguish water sources in discharge (Nimz, 1998). The purpose of this work was to identify the sources and mass input of "1"2"9I and trace the transport, partitioning and mass balance of "1"2"9I over time in a remote watershed. We monitored "1"2"9I and other geochemical and isotope tracers (e.g. δ"1"4C_D_I_C, δ"1"3C_D_I_C, δ"2H, δ"1"8O, etc.) in precipitation and discharge from the Wolf Creek Research Basin (WCRB), a discontinuous permafrost watershed in the Yukon Territory, Canada, and evaluated the use of "1"2"9I as a water end-member tracer. Radiocarbon and geochemical tracers of weathering show that discharge is comprised of (i) groundwater baseflow that has recharged under open system conditions, (ii) spring freshet meltwater that has derived solutes through closed-system interaction with saturated soils, and (iii) active layer drainage. The abundance of "1"2"9I and the "1"2"9I/"1"2"7I ratio correlated with geochemical tracers suggests varying contributions of these three water end-members to discharge. The "1"2"9I concentration was highest at the onset of freshet, reaching 17.4 × 10"6 atoms/L, and likely reflects the lack of interaction between meltwater and organic matter at that time. This peak in "1"2"9I was followed by a decline over the summer to its lowest value. Mass balance calculations of the "1"2"9I budget show that the input to the watershed via precipitation is nearly one order of magnitude higher than the output suggesting that such arctic watersheds accumulate nearly 90% of the annual input, primarily in soil organic matter. Temporal variations in discharge "1"2"9I concentrations correlated with changes in discharge water sources suggesting that "1"2"9I is a promising hydrologic tracer, particularly when used in concert with other stable and radioisotopes. - Highlights: • "1"2"9I behaviour, storage and transport within a watershed are poorly understood. • This is a study of "1"2"9I sources and partitioning in watershed reservoirs over time. • A variety of geochemical and isotope tracers revealed temporal changes in flowpaths. • 88% of the annual "1"2"9I input is stored in organic soils. • "1"2"9I is accumulating and is a useful tracer coupled with "1"4C, "3H and stable isotopes.