IMAGING AMS

The benefits of simultaneous high effective mass resolution and large spectrometer acceptance that accelerator mass spectrometry has afforded the bulk analysis of material samples by secondary ion mass spectrometry may also be applied to imaging SIMS. We are exploring imaging AMS with the addition to the Oxford C-14-AMS system of a scanning secondary ion source. It employs a sub-micron probe and separate apparatus for caesiating sample surfaces to further increase the useful ion yield. The source has been accommodated on the system by directly injecting sputtered ions into the accelerator without mass analysis. They are detected with a range of devices including new Si detectors. Qualitative mass spectra may be easily generated by varying only the post-accelerator analysis magnet. Selected ion signals may be used for imaging. In developing the instrument for bioscience research we are establishing its capability for measuring the lighter elements prevalent in biological tissue. Importantly, the machine can map the distributions of radiocarbon labeled compounds with an efficiency of about 1 parts per thousand. A background due to misidentification of non-C-14 ions as a result of the reduced ion mass filtering is too small to hinder high magnification microscopy.