The ILIAS project for selective isobar suppression by laser photodetachment

Laser photodetachment is the process when the extra electron of a negative ion is removed by means of laser radiation. This can happen only if the photon energyis larger than the electron affinityof the ion. The process can be used in mass spectrometry to selectively suppress unwanted isobars, provided that the electron affinityof the unwanted isobaris lower than that of the isobarunder investigation. At the Ion LaserInterAction Setup (ILIAS) at the University of Vienna laser photodetachment of negative atomic and molecular ions is studied and its applicability for selective isobarsuppression in accelerator mass spectrometry(AMS) is evaluated. The setup provides mass separated beams of negative ions with energies up to 30 keV. Negative ions are produced in a Middleton type cesium sputter ion source, mass selected and overlapped with a strong continuous wave laser beam. In order to extend the interaction time of ions and laser, the ion beam is decelerated to thermal energies in a gas-filled radio frequency quadrupolecooler. For an appropriate choice of the photon energy, unwanted isobarsare neutralized while the isobarof interest is unaffected and remains negatively charged. A description of the ILIAS setup and results from the commissioning phase of the RFQ cooler are presented. Up to 8% ion beam transmission could be achieved after a recent redesign of the extraction system. Furthermore first results of photodetachment experiments of 63Cu− within the RFQ cooler are presented.