Nier-Johnson geometry

{
  "id": "MLC-T-CHM-007941",
  "term": "Nier-Johnson geometry",
  "field": "Chemistry",
  "definition": "A double-focusing arrangement for a mass spectrometer in which ions first pass through a 90-degree radial electric field analyser and then through a 60-degree magnetic sector. The electric analyser works with a symmetrical object and image arrangement, while the magnetic analyser is used asymmetrically. Placing the magnetic sector first instead gives a reversed geometry.",
  "subject": "Physical and Biophysical Chemistry",
  "see_also": [
    "double-focusing mass spectrometer"
  ],
  "references": [
    "Orange Book, 2nd ed., p. 201 (https://media.iupac.org/publications/analytical_compendium/)",
    "PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1546 (https://doi.org/10.1351/pac199163101541)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/nier-johnson-geometry/"
}