Nanogram amounts of selected rare earth elements measured by AMS

Results are presented from a series of measurements on nanogram quantities of selected rare earth elements. The work was performed at the NRL trace element AMS facility using a multi-cathode cesium-sputtering negative-ion source. The possibility to simultaneously inject, transmit and analyze a relatively broad mass range is a unique feature of our AMS system. The detection system, placed in the focal plane of the split-pole magnetic spectrograph, consists of a combination of position-sensitive microchannel plate and ion-implanted Si detectors. The small amounts of rare earth elements to be measured were chemically extracted from the surface of metallic samples. Calibration curves were built using standards containing 3 and 10 ng of the material of interest. Extensive studies were performed to develop a method of normalizing the data by adding known amounts of a given element to the samples and to the standard material. Dedicated software was written to allow for event-by-event data acquisition as well as for data reduction. Results are shown for samples containing from less than 100 pg to almost 10 ng of material with uncertainties of the order of 15%. Further upgrades of the experimental method are underway.