Editing Electron ionization (section)

== History ==
[[File:Arthur Jeffrey Dempster - Portrait.jpg|thumb|Arthur J. Dempster]]
Electron ionization was first described in 1918 by Canadian-American Physicist [[Arthur Jeffrey Dempster|Arthur J. Dempster]] in the article of "A new method of [[Anode ray|positive ray]] analysis." It was the first modern mass spectrometer and used positive rays to determine the ratio of the mass to charge of various constituents.<ref>{{Cite journal|last=Dempster|first=A. J.|date=1918-04-01|title=A new Method of Positive Ray Analysis|journal=Physical Review|volume=11|issue=4|pages=316–325|doi=10.1103/PhysRev.11.316|bibcode = 1918PhRv...11..316D |url=https://zenodo.org/record/2451538}}</ref> In this method, the ion source used an electron beam directed at a solid surface. The [[anode]] was made cylindrical in shape using the metal which was to be studied. Subsequently, it was heated by a concentric coil and then was bombarded with electrons. Using this method, the two [[isotope]]s of [[lithium]] and three isotopes of [[magnesium]], with their atomic weights and relative proportions, were able to be determined.<ref>{{Cite journal|last=Dempster|first=A. J.|date=1921-01-01|title=Positive Ray Analysis of Lithium and Magnesium|journal=Physical Review|volume=18|issue=6|pages=415–422|doi=10.1103/PhysRev.18.415|bibcode = 1921PhRv...18..415D}}</ref> Since then this technique has been used with further modifications and developments. The use of a focused monoenergetic beam of electrons for ionization of gas phase atoms and molecules was developed by [[Walker Bleakney|Bleakney]] in 1929.<ref name="Bleakney1929">{{cite journal|last1=Bleakney|first1=Walker|title=A New Method of Positive Ray Analysis and Its Application to the Measurement of Ionization Potentials in Mercury Vapor|journal=Physical Review|volume=34|issue=1|year=1929|pages=157–160|issn=0031-899X|doi=10.1103/PhysRev.34.157|bibcode = 1929PhRv...34..157B}}</ref><ref name="InghramHayden1954">{{cite book|author1=Mark Gordon Inghram|author2=Richard J. Hayden|title=Mass Spectroscopy|url=https://books.google.com/books?id=o7wrAAAAYAAJ&pg=PA49|year=1954|publisher=National Academies|pages=32–34|isbn=9780598947109|id=NAP:16637}}</ref>