Accelerator mass spectrometry with a gas-filled magnetic spectrograph

A detector system has been set up for accelerator mass spectrometry, especially suited to detect heavy radionuclides. A time of flight measurement allows us to separate ions with respect to their mass. Even for 90Sr a mass resolution of ΔA< or approx.0.3 (FWHM) is achieved. The separation with respect to their nuclear charge is accomplished by deflecting the ions in a gas-filled Q3D magnetic spectrograph with high dispersion. The resolution as observed relative to the displacement for peaks of different isobars corresponds to ΔZ< or approx.1 for the three isotopes studied: 90Sr, 59Ni and 41Ca. In addition, the different energy loss of isobars in the gas is determined by their residual energy in the focal plane detector. Thus concentrations could be measured with sensitivities 90Sr/88Sr≅2x10-11, 59Ni/58Ni≅2x10-11 and 41Ca/40Ca< or approx.10-12. These values can be improved by one to two orders of magnitude. The result for 90Sr allows us already to detect contaminations in samples from the biosphere with activities below 1 Bq/kg within a few hours after the chemical extraction of strontium. (orig.)