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. Isobar separation and suppression were optimized with respect to the gas pressure in the gas-filled magnet and detector, respectively, and with respect to the grid and electrode configuration in the detector.
Our tests were conducted at a terminal voltage of 4.6 MV using combined gas-foil stripping and a 37 MeV 36Cl7+ ion beam. In this case an optimal suppression of the interfering isobar 36S in the stand alone gas-filled magnet was found to be better than a factor 300. An additional 300 times reduction of 36S was achieved by the Eresidual signal of the two anode gas ionization detector. On the other hand, the ΔE signal from the first anode of the detector provided a negligible isobar separation for all tested Ar gas pressures (40-120 mbar) in the 20 cm long detector at the optimal N2 gas pressure of 2.5 mbar in the gas-filled magnet. The isobar separation in the detector is limited by the energy straggling of the ion beam before the detector, which had a major contribution from the gas-filled magnet and minor additions from the entrance windows to the magnet vacuum chamber and to the detector. An overall suppression of 36S in the optimized gas-filled magnet and gas ionization detector was thus found to be at least 105, which is ~100 times better than previously reported for a stand alone gas ionization detector and the same ion energy. Therefore, for samples with a sulfur content of less than ~5 ppm, our gas-filled magnet and gas ionization detector system are capable to measure 36Cl down to the level of 36Cl/Cl ≤10-15, which was also confirmed by measurements on chemically prepared blank samples.
Details about our experiments and results will be presented together with a discussion concerning measurements of 36Cl with a gas-filled magnet and a gas ionization detector at a medium sized AMS tandem accelerator system (~1 MeV/amu).
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)