The Leibniz-Labor AMS facility at the Christian-Albrechts University, Kiel, Germany

Abstract

The AMS facility of the Leibniz-Labor für Altersbestimmung und Isotopenforschung of the Christian-Albrechts Universität is based on a 3 MV Tandetron from High Voltage Engineering Europa (HVEE) with a single cesium sputter ion source and a separator/recombinator for simultaneous injecton of the three isotopic carbon beams. The AMS system is similar to those at the Woods Hole Oceanographic Institution, USA, and the University of Groningen, The Netherland, but it has some new features based on experience at these two facilities. These include improved vacuum seals, beam diagnostics, X-ray and background suppression as well as a more reliable system control through a PLC-unit with a serial line to the main system computer. The open system design of the beam optics allows significant horizontal and vertical movement of the ion beams without loss to the walls of the system. This leads to plateaus in the response of the isotope beams and ratios to changing values of various ion optical elements. Combined with highly stable power supplies, this gives reproducible measurements. The acceptance tests, e.g., showed that Poisson counting statistics at 0.15% and 0.22% respectively, determined the statistical uncertainty in the 14C12C ratios measured for the individual samples of two test series. Strong discrimination of unwanted ions results in low background count rates in the detector, equivalent to an apparent age of 75000 years at present, in spite of the open architecture. Routine measurements since late January 1996 (to late May 1996) have dated 127 unknown samples, mostly foraminifera. The prototype of the carbonate to CO2 conversion system and the graphite system used for the measurements are also described.