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The multiple probable oxidation states of actinide elements can lead to their molecular anions to result in complicated yield patterns from a Cs+ sputter ion source. For actinides AMS, two methods can be practiced in order to concentrate the yields into just one or two anion species. The present common practice has been to avoid excessive oxygen reactions in the sputter targets, so that the mono-oxide anions can be produced with good or applicable ionization efficiencies. However, this method requires the typical 860-type Cs+ sputter ion sources to be operated with relatively high Cs+ fluxes, a condition that not all such sources in use can be operated with lasting stability. On the contrary, with low Cs+ fluxes, good or applicable ionization efficiencies can also be achieved for producing element-specific polyatomic oxide, oxyfluoride, or fluoride anions of actinides, if the sputter targets are aided with dominantly oxidizing or fluorinating matrices. This paper describes a systematic study of such phenomena using ZnO and FeF 3 to form the respective oxidizing and fluorinating matrices. It was found that using the chosen set of polyatomic fluoride anions and the FeO x H y + FeF 3 sputter targets, not only all rare actinides could be measured with low backgrounds matching those using mono-oxides, but also with the available ionization efficiencies fully utilized within a shorter time. A few additional merits are also noted. [ABSTRACT FROM AUTHOR]

The Lalonde 3MV-AMS system uses one large injection magnet and one large high energy magnet, providing both sufficient bending power and resolution in both the low and high energy mass and charge systems for all heavy elements. This allows two demanding AMS subjects to be investigated conclusively: one is the search for the elusive atomic negative ion Yb−, and the other is the use of 236UF 5 − to achieve sub-10−13 abundance sensitivities with a single analyzing magnet in the high energy system. Both studies require the AMS system to be capable of sufficiently removing intense E/q and EM/q2 interferences to the rare signals. In the case of the Yb− search, the complication caused by the fragmenting ytterbium hydride beams must be well resolved; in the case of 236U detection, its relative mass difference from the abundant 235,238U is among the smallest of all cases in AMS. In carrying out these investigations, a generalized method of analyzing the potential E/q and EM/q2 interferences in AMS is illustrated. The conclusions are: (1) With 12 kV ion source extraction voltage and 0.5 MV accelerator terminal voltage, which correspond to a maximum electric field gradient of 2.8 kV/cm along the ion trajectory from the sputter target surface to the entrance of the accelerator terminal, Yb− has not yet been observed by AMS using a Cs+ sputter ion source. (2) A best-possible abundance sensitivity of 236U/U ∼ 4 × 10−14 has been indicated using UF 5 − with just one large magnet in the high energy system. [ABSTRACT FROM AUTHOR]

The analysis of 135 Cs/Cs ratios at levels below 10 −12 by accelerator mass spectrometry (AMS) would preferably use commonly available negative ion injection systems. The sputter ion sources in these injectors should ideally produce currents of Cs − or Cs-containing molecular anions approaching μA levels from targets containing mg quantities of Cs. However, since Cs is the most electro-positive stable element in nature with a low electron affinity, the generation of large negative atomic, or molecular beams containing Cs, has been very challenging. In addition, the reduction of the interferences from the 135 Ba isobar and the primary 133 Cs + beam used for sputtering are also necessary. The measurement of a wide range of the isotope ratios also requires the ion source memory of previous samples be minimized. This paper describes some progresses towards a potential solution of all these problems by recycled sputtering using fluorinating targets of PbF 2 with mg CsF mixed in. The problems encountered indicate that considerable further studies and some redesign of the present ion sources will be desirable. [ABSTRACT FROM AUTHOR]

Typical accelerator mass spectrometry (AMS) ion sources readily produce useable currents of a wide variety of negative ions, including exotic species, and the sensitivity and dynamic range of AMS can be used for relatively unambiguous ion identification at low count rates. Difficulty producing negative ion currents with high fluxes (ex. when electron binding energies are small) and unambiguous identification of reaction products can be obstacles to negative ion-gas reaction studies. Thus, an AMS setup can be considered to be suitable for certain ion-gas reaction studies. Presented here are preliminary studies on interactions of SrF 3 − , YF 3 − , ZrF 3 − , YF 4 − and ZrF 5 − with NO 2 gas at <50 eV kinetic energies using a prototype radio-frequency quadrupole (RFQ) instrument installed before the accelerator on the low-energy side of an AMS system. The superhalogen anions SrF 3 − , YF 4 − and ZrF 5 − were found to be highly unreactive with NO 2 , consistent with expected electron binding energies greater than 3.6 eV. YF 3 − and ZrF 3 − were found to have large overall attenuation cross sections in NO 2 of 7.6 × 10 −15 ± 4.4% cm 2 and 1.5 × 10 −14 ± 21% cm 2 respectively at the ion energies created under the experimental conditions. The major reaction channels were shown to be electron transfer and oxygen capture. A cluster NO 2 ·(YF 3 − ) was also observed. [ABSTRACT FROM AUTHOR]

Currently analysis of 36 Cl by accelerator mass spectrometry (AMS) requires large facilities for separation of the isobar 36 S. Previously, it has been shown possible to suppress S − by >6 orders of magnitude at low energies in a prototype radio-frequency quadrupole (RFQ) instrument by ion reactions in NO 2 gas in the injection line of an AMS system. Reaction products for the negative ions S − , SO − and Cl − with NO 2 , and S − with N 2 O, have been surveyed in order to understand isobar attenuation plateaus and the losses of analyte ions. Ion energies were at eV levels, but had a large initial energy spread of at least several eV. Under these conditions, the aggregate total S − and SO − cross sections in NO 2 were estimated to be 6.6 × 10 −15 cm 2 and 7.1 × 10 −15 cm 2 respectively and the major reaction channel observed was electron transfer producing NO 2 − . Other reaction products observed for S − were SO − , SO 2 − , NS − , and NSO 2 − . On the other hand, S − , SO − and NS − were found to be largely unreactive with N 2 O despite the existence of some highly exothermic reaction channels. When Cl − was injected into NO 2 , reaction products such as ClO − and NO 2 − were observed only at low levels suggesting that larger Cl − transmissions should be possible with some RFQ design modifications. The ClO − reaction product had only a small attenuation under the experimental conditions, despite having near resonant electron affinity with NO 2 . [ABSTRACT FROM AUTHOR]

Abstract: Using targets made with PbF2 matrices, Cs+ sputter sources have been found to yield element-specific patterns of molecular fluoride anions that may be used to enhance the mass spectrometry of certain elements. While the patterns are found similar for all lanthanides and the heavier actinides, substantial differences are found for the lighter actinides. In the case of Pu and U, of all their fluoride anions, and are produced with the highest yield. Mass spectrometry of Pu using can provide a partial chemical separation in the ion source, as the yield of is two orders of magnitude lower than that of the . This, in turn, reduces scattering of U ions when measuring Pu in the high-energy components of the AMS system. This instrumental reduction of U is advantageous in cases that require rapid Pu analyses as it simplifies the chemistry of Pu/U separation and other steps in the sample processing. In this procedure, Pu can be co-precipitated with another element as a fluoride, which is then mixed with a sufficient amount of PbF2 powder to form a sputter target. A series of tests were carried out and NdF3 was identified as one such suitable carrier. Measurements of Pu+3 at ∼0.85MV terminal voltage showed that the 239,240,241,242Pu isotopes can be detected with a manageably low background, high efficiency and a 1fg detection limit. Preliminary tests were carried out using the existing IsoTrace AMS system, modified only by the addition of electronic controls to automatically adjust the terminal voltage and all high-energy electric analyzers, along with the injection magnet bouncer. However, both the injection and detection systems were not designed for this task, so considerable room is available for reducing the detection limit into the ag range with modern AMS systems – such as the one being commissioned at University of Ottawa. [Copyright &y& Elsevier]

Abstract: A study of fluoride anion formation in PbF2 matrices in a Cs+ sputter source shows that, for transition metals Groups 3, 4 and 5, distinctively large currents (similar to PbF3 −) of their corresponding superhalogen anions can be produced by Cs+ sputter sources. This trend however, quickly breaks down for elements from Group 6 towards 12. The phenomenon can be understood as a competitive outcome of fluorination reactions among lead, caesium and transition metals, as their fluorine-binding energies generally decrease from Group 3 to 12. Therefore, if a strong fluorine-binding element, such as Mo, coexists with Ru in a fluorinated matrix, the formation of 99RuF4 − can be significantly suppressed relative to MoF4 − and 99TcF4 −, a possible superhalogen anion of Tc. This phenomenon is indeed observed with a neutron irradiated Mo sample that contains trace levels of both 99Tc and Ru, leading to a possible matrix-assisted method for 99Tc analysis using small and large accelerators. [Copyright &y& Elsevier]

Abstract: Using AMS as high-sensitivity SIMS, the relative sputter yields of (n =0–8) from Cs+ sputtered PbF2 matrices have been systematically assessed for most elements. M represents an element, which is either embedded into or already present at low levels in PbF2 matrices. The powdered crystal PbF2 is found to become electrically conducting in a Cs+ sputter source and, in this environment, an effective F and F− donor in near surface chemical reactions. This ensures that the surface reactions leading to the observed generally occur under the condition of abundant F/F− reactants, maximizing the intensities of the fluoride anions that in general have electron binding energies greater than that of Cl−. In the chemical literature, these anions are known as superhalogen anions . [Copyright &y& Elsevier]

Abstract: The anion is found to be produced from a Cs+ sputter source with a relative yield of ∼10−4 of , the superhalogen anion of K in the target. Therefore, from CaF2 samples, is probably the dominant molecular ion by which 41K background is introduced in AMS measurements of 41Ca using . Evidence is found that a source of K is the impurities in the Cs used for sputtering. The next most important molecule generating 41K background is probably 41K57Fe− due to the presence of iron in the parts of the ion source. The use of collision induced dissociation (CID) for separating and has been investigated. The anion has been shown to be reduced with respect to , by three orders of magnitude using CID at eV energies using the Isobar Separator for Anions (ISA) described in Ref. . This is a degree of isobar discrimination sufficient for making very-low level 41Ca measurements using small accelerators without the need of additional dE/dx measurement. [Copyright &y& Elsevier]

Abstract: During tests with BeF2 samples in a sputter ion source, it was found that the largest negative fluoride ion current was of . This is because BeF3 belong to an extensive class of molecules known as super-halogens. These have electron affinities much higher than those of the halogens themselves and so are of great potential interest to AMS. A systematic study of anions of this class for Li, Be and B was therefore undertaken. The strongest fluoride anions measured were , and as expected. The anion of LiF3 could not be observed at a ratio of . The anion of BF3, which is predicted like the anion of BF to be unstable, was observed with intensity modestly greater than that of the BF anion. These measurements illustrate some general properties of super-halogen anions: (1) their great electron binding energies make it possible to produce large currents with Cs+ sputter sources; and (2) the super-halogen anions of the neighbouring elements are often one halogen atom apart, so some degree of isobar selectivity is available at the ion source. The possibility of directly counting 7Be2+ at <2MV terminal voltage, by simply injecting , is an example of this realization. Other ramifications of super-halogen anions for low energy AMS development are also discussed. [Copyright &y& Elsevier]

The isobar separator for anions (ISA) was used together with a 3 MV tandem accelerator mass spectrometer (AMS) to demonstrate the real time (on-line) separation of Te − from I − . Following the ion source mass spectrometry and major retardation to tens of eV, the ISA uses a radiofrequency quadrupole (RFQ) ion guide to confine and direct I − and associated Te − isobar anions through a gas-reaction cell, where chemical reactions occur at eV energies with the electronegative gas NO 2 . Anions are subsequently reaccelerated out of the ISA to near original ion source extraction energies for AMS analysis. At 5 mTorr NO 2 in the ISA gas-reaction cell, 125 Te − was observed to be attenuated by a factor of ∼10 7 as compared to 127 I − that did not experience significant (<50%) losses. A comparative test using 37 Cl − and 32 S − (having similar chemical properties to iodine and tellurium) showed a 32 S − attenuation of >10 7 relative to 37 Cl − under the same ISA–AMS conditions. The preferential destruction of Te − (and S − ) at eV energies in the ISA is likely due to a larger favorable destruction cross-section with NO 2 . This study is the first demonstration of I–Te anion separation for AMS, and makes possible the use of 125 I, free of the contaminant 125 Te isobar after suitable sample purification, for future 129 I/ 125 I carrier-free analyses of natural samples at ultra-low trace levels. [ABSTRACT FROM AUTHOR]