A dispenser for supplying metal vapour to an ion source. The metal is provided in a capsule 17 which may be broken to release the metal by turning knob 16 which causes a capsule housing 12 to move to the right, thus causing the capsule to break against a piston member 21. The piston member 21 communicates with a conduit 3 which in turn communicates with the associated ion source, partly shown under reference 2. A heating mantle 29 is provided to vapourise the metal in the housing 12 so that it can pass from the dispenser, through conduit 3, to the ion source.