A microbeam negative ion source based on a modified HICONEX™ source

The first stage of the development of AUSTRALIS, a microbeam AMS system at the HIAF laboratory at North Ryde, Sydney has been completed. The system is designed to enable in-situ microanalysis of geological samples for ultra-traces and for isotropic data for minerals exploration research. The negative ions for analysis are produced by sputtering with a microbeam of Cs+. This primary microbeam source was developed by modifying a General Ionex model 834 HICONEX ion source and combining it with auxiliary cylindrical lenses. The Cs beam bombards the sample at 45° incidence angle and the secondary ions are extracted at normal angle. The source features a novel intermediate or “screen” electrode to correct for the effect of the secondary ion extraction field on the trajectory of the primary beam, in order to bring the primary beam to the geometric centre. The high energy analysis system of AUSTRALIS features a pair of deflector systems to permit fast switching of isotopes without altering the magnet setting. The paper describes the initial testsʹ results showing good agreement with the design parameters.