129I-AMS by a 97Mo16O2 molecular pilot beam method

An 129I-AMS system has been developed on the 12UD tandem accelerator at the Tandem Accelerator Complex, University of Tsukuba using a 97Mo16O2 molecular pilot beam method developed at the complex. The acceleration voltage of the tandem is precisely controlled and kept within 0.1% accuracy for several days under the 97Mo16O2 molecular pilot beam method. This stability is enough to maintain a stable transmission of 129I ions through the tandem accelerator. Simultaneously generated 127I negative ions are measured by a Faraday cup installed just after a bending magnet for the ion source. Both 129I− and 97Mo16O2- ions are accelerated concurrently and the resultant 129I12+ and 97Mo9+ ions are transported to an AMS beam line. A second stripper foil sweeps out the 97Mo9+ ions from the AMS beam line. The 129I26+ ions are selected over the Mo ions for detection using a pair of magnetic and electrostatic deflectors. Finally, 129I26+ ions are clearly detected using a SSD detector, with no strong background. The accelerator voltage is set to 9.68 MV in order to get the most efficient yields of both 129I12+ and 129I26+. The ratio of the background level of 129I to 127I is ∼1 × 10−13.