Implementing a SIMS ion source on the NRL trace element accelerator mass spectrometer

The NRL trace element accelerator mass spectrometer facility has recently added a modified Cameca IMS 6F SIMS instrument as a highperformance ion source, providing the advantages of accelerator mass spectrometry to SIMS analysis. These advantages include removal of molecular interferences, a greatly reduced background, and composition analysis using molecular ions (after breaking them into atomic constituents before detection). This last feature compensates for a requirement to use only negative secondary ions, as it enables measurement of electropositive elements. In addition, the NRL facility provides for parallel mass analysis, thus improving isotope ratio precision and practical sensitivity. Spatial analysis of the sample is still provided by raster of the primary Cs beam. The modified Cameca includes the Cs primary column, sample chamber, and the secondary ion column up to the standard electrostatic analyzer. The NRL accelerator facility supplants the normal mass spectrometer portion of the IMS 6F instrument. Additional recent facility upgrades provide improved mass spectrometry performance, both for a prior radiocarbon ion source and the now installed SIMS. An example measurement, using silver ions, demonstrates the system’s capabilities