Improvements in or relating to ion sources for mass spectrometers
Reference is made to ion sources suitable for use with gaseous samples, such as UF/sub 6/. Such a gas may attack the electrodes of a mass spectrometer ion source or react with substances adsorbed on the electrode surfaces, and the reaction products may cause change in the source characteristics in a random manner. The useful life of the source between clean-ups is limited by these effects, and varies as its sensitivity. Low sensitivity requires increased sample flow for measurements, with increased build-up of insulating film. It is therefore desirable to use a form of source that does not rely mainly, as hitherto, on the action of a slit in a collimating electrode on a divergent ion beam in order to define the final beam. A large proportion of the initial ions is captured by the collimating electrode in such an arrargement and do not enter thc magnetic analyzer. In the form of ion source described an ionizirg region is provided within which substantially all ion formation is effected. Spaced therefrom are first and second electrodes, a focussing electrode and a collimating electrode, all with slits for the passage of ions from the ionizing region. The electrodes are dimensioned and spaced in relation to the potentials applied to them, that after a cross-over approximately in the plans of the first electrode an image of the ionizing region is formed on the incident side of the second electrode, and a divergent beam therefrom, leaving the second electrode, is caused by the focussing electrode to provide at the collimating electrode a beam whose width is only slightly greater than the width of the slit therein. The ionizing region may comprise means for forming ions from a gas by bombardment with an electron beam directed transversely to the source axis. The potential applicable to the focussing electrode may be such that the second electrode acts as a strong convergent lens and the very slightly divergent beam leaving the second electrode is caused by the divergent action of the focussing electrode to direct a slightly divergent beam towards the collimating electrode. (UK)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-29-005247
- OSTI ID:
- 4387854
- Report Number(s):
- GB 1328882
- Resource Relation:
- Patent File Date: 1970 May 01; Other Information: Orig. Receipt Date: 30-JUN-74; Bib. Info. Source: UK (United Kingdom (sent to DOE from))
- Country of Publication:
- United Kingdom
- Language:
- English
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