Determination of 3He with a tandetron accelerator at 0.8 MV

A measurement of 3He in natural gas was carried out using a 1 MV tandetron accelerator at 0.8 MV terminal voltage and an rf ion source. To eliminate interfering backgrounds of H3, HD and 3H, helium ions in charge state 2+ were selected. The 3He/4He ratio in the helium gas was measured to be 1.4x10-7. The background originating from 4He2+ ions through charge changing processes in the residual gas of the accelerator and scattering in the switching magnet was removed completely with an Al absorber in front of the detector. The sensitivity for determining the 3He/4He ratio was better than 10-10. (orig.)