Term: Nier–Johnson geometry
https://doi.org/10.1351/goldbook.N04141

Definition:
An arrangement for a double-focusing mass spectrometer in which a deflection of π 2 radians in a radial electrostatic field analyser is followed by a magnetic deflection of π 3 radians. The electrostatic analyser uses a symmetrical object-image arrangement and the magnetic analyser is used asymmetrically.

Related Terms:
1) double-focusing mass spectrometer (http://doi.org/10.1351/goldbook.D01845).

Source: Orange Book, 2nd ed., p. 201 (https://media.iupac.org/publications/analytical_compendium/)

Citation: 'Nier–Johnson geometry' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.N04141

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