GB1064142A - Improved mass spectrometer - Google Patents

Abstract

1,064,142. Mass spectrometers. LEYBOLD HOLDING A.G. Oct. 9, 1963 [Oct. 9, 1962]. No. 39902/63. Heading HID. A mass spectrometer for analysis and leak detection is in the form of a cylindrical capacitor immersed in a uniform, constant, axial magnetic field, is provided with means for introducing ions of the gas to be analysed into both fields at a place spaced from the inner electrode, and is operated with the inner electrode as the cathode. Cylindrical electrodes 3, 4 are provided with end plates 2, 22, and screen electrodes 5, 6, 51, and 61, maintained at potentials appropriate to their diameter. Ions are either introduced from an external source through a window in the outer electrode, or are produced in the latter's immediate vicinity by an electron beam directed parallel to the capacitor axis just within the outer electrode. The fields are arranged such that all ions heavier than that which it is desired to detect hit the central electrode, secondary electrons produced by the latter being removed by a small potential difference maintained between the screen electrodes 5 and 51. Ions of desired masses pass out through windows, disposed at corresponding angular positions in the outer cylinder, to collector electrodes and D.C. amplifiers. In an alternative construction (Fig. 3, not shown) the screen electrodes extend the whole length of the capacitor and have apertures aligned with the windows in the outer electrode. In an alternative method of operation, orbiting ions of desired mass accumulate until deflected by collision or space charge, their pressure being detected by a high-frequency amplifier connected across the capacitor electrodes: a highfrequency signal corresponding to the resonance frequency of the desired ions is employed to modulate the ion source or ion-producing electron beam, or is applied across a pair of supplementary electrodes located near the outer electrode. To permit separation of the signal arising from heavier-than-desired ions from the modulated ion source or electron beam striking the inner electrode, the latter is formed in two separate portions (Fig. 2, not shown), facing towards and away from the ion source respectively, the current flowing in the latter portion permitting measurement of the ions of desired mass.