GB888887A - Apparatus for producing negatively charged polyatomic compounds by electron attachment and analysing the same by mass spectrography or mass spectrometry - Google Patents

Abstract

888,887. Heavy-ion-beam tubes. VAKUTRONIK VEB. March 3, 1959 [April 25, 1958], No. 7439/59. Class 39(1) An ion source for producing negatively charged, but undissociated, relatively large and complex polyatomic molecules for subsequent analysis in a mass spectrometer consists of a low pressure discharge chamber 1 with one or more hot cathodes 2 in which a substantially neutral plasma having a low electron temperature and a low potential gradient is formed in an auxiliary gas of low ionizing voltage, e.g. caesium vapour, mercury vapour or argon. The plasma is magnetically constricted in a non-uniform magnetic field set up between asymmetrical pole-pieces 4, 15. Pole-piece 15 is also the discharge anode and pole-piece 4 is also an intermediate electrode. Immediately in front of pole-piece 15 is the ion emission slit 10 and the test gas or vapour is introduced in front of the slit 10 e.g. by evaporation from a movable and electrically heatable crucible 9, through the agency of a sharply directed gas or vapour stream, or mechanically by means of ultra-sonic oscillators or other vibrating surfaces. Several crucibles 9 or a multiple channel gas radiator may be provided. One crucible includes a calibration substance. The ion emission slit 10 is covered by a pre-diaphragm 14 and is movable by an amount greater than the diameter of the prediaphragm. The ions passing through the slit 10 subsequently pass through by an accelerating electrode 17, auxiliary aperture diaphragm 21 and adjustable main aperture diaphragm 22, cylindrical lens 23 and separating magnet chamber 33 of the spectrometer. The target chamber forms an ion image tube 30 and includes an adjustable photographic plate 27, a secondary emission cathode 28 and an aluminized fluorescent screen 31. Electrons removed with the molecular ions fall on a plate 26 in the vicinity of the entry of the beam into the magnetic field, the plate being screened with lead to prevent the X-rays generated from affecting the fluorescent screen. The ion beam is directed on to the apertures in diaphragms 21, 22 by means of a pair of deflecting plates 18 behind the ion emission slit 10.