Long-Lived Noble-Gas Radionuclides

The first AMS measurements of Ar-39 and Kr-81 have been performed by combining positive-ion production in an ECR ion source with acceleration to 6 MeV/A in the ATLAS linear accelerator and detection in a gas-filled spectrograph. Sensitivities of Ar-39/Ar = 8 x 10(-16) (natural argon), and Kr-18/Kr = 2 x 10(-10) (neutron-activated krypton)were achieved. A full-stripping experiment for Kr-81-Br-81 separation at 45 MeV/A was performed with the MSU K1200 cyclotron. Substantial contributions from nuclear reactions in a Be stripper foil were observed, in the attempt to detect Kr-81(36+) ions in the A1200 recoil separator. The general situation for the detection of noble gas radionuclides is discussed.