A primary ion source subassembly for use with a secondary ion mass spectrometer may include a unitary graphite ionizer tube and reservoir base. A primary ion source may include a capillary insert defining an ionizer aperture. An ionizer aperture may be centrally arranged in an outwardly protruding conical or frustoconical surface, and may be overlaid with a refractory metal coating or sheath. Parameters including ionizer surface shape, ionizer materials, ionizer temperature, and beam stop plate orifice geometry may be manipulated to eliminate ghost images. A graphite tube gasket with a dual tapered surface may promote sealing of a source material cavity.