Search

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]

Based on the encouraging results of our initial efforts to develop a 90Sr accelerator mass spectrometry capability, we have undertaken efforts to enhance our system. By changing some key operating parameters and constructing an optimized detector we were able to improve the discrimination of 90Sr from the isobaric interference 90Zr and reduce our instrumental background by nearly two orders of magnitude. Our current background (4 × 106 atoms, 3 mBq) is comparable to that achievable by decay counting, but is still a factor of ten higher than what is theoretically predicted based on the efficiency of our system. Therefore, future plans include implementation of a time-of-flight system to improve the rejection of 90Zr. [ABSTRACT FROM AUTHOR]

By making modifications to our previously established measurement setup, we increased our abundance sensitivity for 233U by three orders of magnitude and can now measure 233U/238U ratios as low as 10−13. Because 233U has separate production pathways than 236U, it can provide valuable information on the particular source of anthropogenic uranium in a sample. We demonstrated the utility of our improved capability by using 233U to distinguish separate sources of anthropogenic uranium in a set of samples collected from a contaminated site. In the future, we plan to apply our new capability to characterizing 233U in a wide range of uranium materials. [ABSTRACT FROM AUTHOR]

A gas-fed negative ion source for use in an accelerator mass spectrometry system has been built at the United States Naval Research Laboratory. This ion source is a filament driven plasma ion source using a multicusp magnet arrangement for plasma confinement. Our specific design was assisted by modeling using the SIMION code to optimize beam extraction optics. In addition to the ion source modeling, preliminary characterization of the plasma behavior was performed, which showed the typical and expected order of magnitude increase in collected plasma current when a multicusp magnetic arrangement is employed versus the case with no magnets. Future work will involve implementing a Langmuir probe for more detailed characterization of the plasma, investigation of the effects of using a symmetric rather than a multicusp magnet arrangement, and ultimately the extraction and characterization of ion beams from the source. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]