Abstract: Mass spectrometer having an ion source, acceleration means able to impart to the ions an energy essentially dependent on their electric charge, means for producing in a sector a magnetic field orthogonal to the plane of the trajectory of the ions in order to inwardly curve said trajectory and means for detecting the ions. At the inlet of the magnetic sector are provided electrostatic means able to modify the tangential velocity of the ions and consequently their energy, in such a way that ions with different masses can, at different times, follow the same inwardly curved trajectory in the magnetic sector.

Abstract: The invention provides a process and device for the ionic analysis of an insulating sample brought to a given negative potential, of the type in which a target on the surface of the sample to be analyzed is bombarded by means of a primary electron beam and negative ions emitted by the bombarded target are used for producing an ion image of the sample. An electron beam whose normal speed component cancels out just at level of the surface of the target is directed perpendicularly to the target.The device comprises for this purpose a filament, brought substantially to the same negative potential as the sample, which emits the electron beam. The electron beam, after emission, is deflected by a magnetic prism so as to be brought into coincidence with the optical axis of the negative ion beam emitted by the target.