Coaxial reentrant ion source for surface mass spectroscopy

An improved ion source for characterization of a surface of a sample including a housing oriented about a central axis, Z; a magnet cooperatively disposed within the housing for producing a magnetic field along the Z axis direction an anode radially disposed within the housing and within the magnetic field of the magnet that defines an annular ionization chamber having an open annular space and further forming a central tubular space about the Z axis; a cathode cooperatively disposed at the anode and within the annular ionization chamber; an extractor grids means cooperatively disposed within the housing so as to form a boundary of the ionization chamber; annular focusing rings disposed on the housing and externally to the extractor grids for focusing ions emerging therefrom; neutralizer filament cooperatively disposed with focusing rings; a central lens cooperatively disposed about the central axis Z in the central tubular space formed by the anode and adapted to accept ions and neutrals emanating from a sample; an entrance grid disposed at the sample end of the central lens; a second ionizer disposed along the length of the central lens; an exit grid for directing ions toward a measurement instrument such as a mass spectrometer; and an input gas pipe cooperatively disposed with the housing and anode so as to supply gas to the ionization chamber. A shield is preferably used to shield the apparatus from electromagnetic interference.