Selective isobar suppression for accelerator mass spectrometry and radioactive ion-beam science

A new method of selective isobar suppression by photodetachment in a radio-frequency quadrupole ion cooler is being developed at HRIBF with a twofold purpose: (1) increasing the AMS sensitivity for certain isotopes of interest and (2) purifying radioactive ion beams for nuclear science. The potential of suppressing the 36S contaminants in a 36Cl beam using this method has been explored with stable S− and Cl− ions and a Nd:YLF laser. In the study, the laser beam was directed along the experiment’s beam line and through a RF quadrupole ion cooler. Negative 32S and 35Cl ions produced by a Cs sputter ion source were focused into the ion cooler where they were slowed by collisions with He buffer gas; this increased the interaction time between the negative-ion beam and the laser beam. As a result, suppression of S− by a factor of 3000 was obtained with about 2.5 W average laser power in the cooler while no reduction in Cl− current was observed.