Measurements of 36Cl with a gas-filled magnet at the Uppsala tandem laboratory

The performance of a gas-filled magnet combined with a gas ionization detector for measurements of 36Cl was systematically studied at the Uppsala tandem laboratory. Our tests were conducted at a terminal voltage of 4.6 MV using gas-foil stripping and a 37 MeV 36Cl+7 ion beam. An optimal suppression of the interfering isobar 36S in the stand-alone gas-filled magnet (2 mbar N2 gas pressure) was found to be ⩾300, and an additional ⩾300 times reduction was achieved by the Eresidual signal of the two-anode gas ionization detector. The overall suppression in the order of ⩾105 permits analysis of samples with a sulfur content of ⩽5 ppm and 36Cl/Cl ratios of ⩾10−15. We have successfully measured samples with 36Cl/Cl ratios in the range of 10−12–10−15 demonstrating the use of a medium-sized tandem accelerator system (∼1 MeV/amu) for 36Cl AMS.