The installation of the new PRIME Lab ion source instantly increased performance at our facility. While the old source averaged about 184ηA of 13C, the new source was able to give an output of 1080ηA. Several improvements have been made since the new source has gone online made a significant impact on the overall output currents. The first obstacle discovered was the cesium would get clogged in the feed-through tube. To alleviate this problem the thermal conductivity of the tube was increased by changing the material from stainless steel to copper and the exit orifice of the tube was enlarged. Our new source incorporated a larger ionizer with a commensurate increase in the ionizer-cathode distance. However, the ionizer hole was initially kept the same diameter as the opening on the original ionizer. It was found that some of the secondary beam impinged on the ionizer and the hole had to be enlarged. Another increase in current was achieved by changing the way the cesium vapor deposited on the ionizer. The initial design had the cesium shroud exit passages aimed at the center of the ionizer. Simulations and experiment both indicated that cesium deposited near the ionizer hole would miss the sample. Thus, the angle was made steeper and more of the cesium was able to hit the section of the ionizer between the exit hole and the outer edge. The last test with 13C, (reactor graphite only) indicated that currents of 800-900ηA of beams were possible for extended periods of time. Besides increased currents, another feature of the new source is a lack of cross contamination or memory between samples. Blanks have been unaffected by unknowns that had isotope ratios 4 or 5 orders of magnitude higher than the measured blank value. Finally, the new sample changer allows us to run continuously without breaking vacuum or turning off power supplies.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)