Future of the NOSAMS Tandetron AMS system

The NOSAMS 3 MV Tandetron AMS system will soon reach its 20th anniversary of operation. A critical review of all aspects of the system is necessary to assess the analytical, economical and operational factors that enter into the consideration of either an upgrade or a replacement of the instrument. Recent in-house experience with the design and construction of a large-acceptance (14)C AMS system gives us a benchmark with which to compare the expected outcome of an upgrade. The present ion analysis efficiency of our Tandetron system is roughly 1%, well below the 4% value of our new system. This affects the lower limit of analyzable sample size, speed of analysis, exposure to systematic errors, and the upper limit of achievable single-sample counting statistics. At first glance it may seem obvious that a replacement (even at higher cost) would be preferable to an upgrade. However, it will be shown that there are good reasons to consider the latter. One of the most compelling is the fact that the Tandetron is a state-of-the-art and superior high-current accelerator design with minimal signs of aging and very low-maintenance. Ion beam modeling calculations show that the main transmission limitation of the instrument is caused by the design of our injector, a four-magnet "Recombinator", making it difficult to perform reliable AMS with negative currents exceeding 80 mu A. To be acceptable, an upgrade should bring the Tandetron to at least 3% ion efficiency by replacing the injector with a properly matched high-transmission device. (C) 2009 Elsevier B.V. All rights reserved.