Abstract: An electron source includes a cathode electrode having an emitter of conical shape. A first insulating film surrounds the emitter. A first extracting electrode disposed on the first insulating film draws out electrons from the emitter. A second insulating film is disposed on the extracting electrode and a focusing electrode is disposed on the second insulating film for focusing the electrons. The films and electrodes are hollowed to constitute a well surrounding the emitter, and the electrodes are applied predetermined voltages respectively to control the electrons emitted from the emitter. A disturbance that the voltage applied to the focusing electrode causes to the electric field around a summit of the emitter is suppressed. The electrode source may be made by determining a thickness of a masking material so that, when forming the conical emitter, an area occupied by the films deposited on the masking material in the well is smaller than the well when all the films have been completed.

Abstract: A method for determining the concentration of a monitored gas in the head space of a confined space containing a medium material at a given temperature (T.sub.1), includes the steps of: (a) providing an extracting apparatus having a chamber for receiving a sample volume of the material to be extracted from the confined space; (b) controlling the temperature of the chamber such that the temperature of the chamber is maintained at the given temperature (T.sub.