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Abstract: Most accelerator mass spectrometry measurements of 26Al utilize the Al− ion despite lower source currents compared with AlO− since the stable isobar 26Mg does not form elemental negative ions. A gas-filled magnet allows sufficient suppression of 26Mg thus enabling the use of the more intense 26AlO− ion. However, most AMS systems do not include a gas-filled magnet. We therefore explored the feasibility of suppressing 26Mg by using a post-accelerator stripping foil. With this approach, combined with the use of alternative cathode matrices, we were able to suppress 26Mg by a factor of 20. This suppression was insufficient to enable the use of 26AlO−, however further refinement of our system may permit its use in the future. [Copyright &y& Elsevier]

Abstract: Strontium-90 is one of the most hazardous materials managed by agencies charged with protecting the public from radiation. Traditional radiometric methods have been limited by low sample throughput and slow turnaround times. Mass spectrometry offers the advantage of shorter analysis times and the ability to measure samples immediately after processing, however conventional mass spectrometric techniques are susceptible to molecular isobaric interferences that limit their overall sensitivity. In contrast, accelerator mass spectrometry is insensitive to molecular interferences and we have therefore begun developing a method for determination of 90Sr by accelerator mass spectrometry. Despite a pervasive interference from 90Zr, our initial development has yielded an instrumental background of ∼108 atoms (75mBq) per sample. Further refinement of our system (e.g. redesign of our detector, use of alternative target materials) is expected to push the background below 106 atoms, close to the theoretical limit for AMS. Once we have refined our system and developed suitable sample preparation protocols, we will utilize our capability in applications to homeland security, environmental monitoring and human health. [Copyright &y& Elsevier]

Understanding plutonium (Pu) sorption to, and desorption from, mineral phases is key to understanding its subsurface transport. In this work we study Pu(IV) sorption to industrial grade FEBEX bentonite over the concentration range 10 −7 –10 −16 M to determine if sorption at typical environmental concentrations (≤10 −12 M) is the same as sorption at Pu concentrations used in most laboratory experiments (10 −7 –10 −11 M). Pu(IV) sorption was broadly linear over the 10 −7 –10 −16 M concentration range during the 120 d experimental period; however, it took up to 100 d to reach sorption equilibrium. At concentrations ≥10 −8 M, sorption was likely affected by additional Pu(IV) precipitation/polymerization reactions. The extent of sorption was similar to that previously reported for Pu(IV) sorption to SWy-1 Na-montmorillonite over a narrower range of Pu concentrations (10 −11 –10 −7 M). Sorption experiments with FEBEX bentonite and Pu(V) were also performed across a concentration range of 10 −11 –10 −7 M and over a 10 month period which allowed us to estimate the slow apparent rates of Pu(V) reduction on a smectite-rich clay. Finally, a flow cell experiment with Pu(IV) loaded on FEBEX bentonite demonstrated continued desorption of Pu over a 12 day flow period. Comparison with a desorption experiment performed with SWy-1 montmorillonite showed a strong similarity and suggested the importance of montorillonite phases in controlling Pu sorption/desorption reactions on FEBEX bentonite. [ABSTRACT FROM AUTHOR]

Precipitation of α′ in Fe Cr alloys under neutron irradiation is thermodynamically driven while being accelerated by radiation-enhanced diffusion. However, similar alloys under ion irradiation at high dose rates (> 10 − 4 dpa/s) fail to exhibit α′ precipitation. Here, the microstructure of an Fe 18Cr alloy under ion or neutron-irradiation at 300 °C at dose rates from ~ 10 − 7 to 10 − 4 dpa/s was analyzed by atom probe tomography. The steady-state composition content of the clusters depends on the ion irradiation dose and dose rate, confirming the contribution of ballistic mixing in diluting the Cr concentration in non-equilibrium α′ precipitates. [ABSTRACT FROM AUTHOR]

Abstract: Modeling of nuclear reactor fuel burnup indicates that the production of samarium isotopes can vary significantly with reactor type and fuel cycle. The isotopic concentrations of 146Sm, 149Sm, and 151Sm are potential signatures of fuel reprocessing, if analytical techniques can overcome the inherent challenges of lanthanide chemistry, isobaric interferences, and mass/charge interferences. We review the current limitations in measurement of the target samarium isotopes and describe potential approaches for developing Sm-AMS. AMS sample form and preparation chemistry will be discussed as well as possible spectrometer operating conditions. [Copyright &y& Elsevier]