Preliminary studies of Pu measurement by AMS using PuF4-

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, PuF4- and UF5- are produced with the highest yield. Mass spectrometry of Pu using PuF4- can provide a partial chemical separation in the ion source, as the yield of UF4- is two orders of magnitude lower than that of the UF5-. 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 ∼0.85 MV terminal voltage showed that the 239,240,241,242Pu isotopes can be detected with a manageably low background, high efficiency and a 1 fg 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.