Doctoral Dissertations


Yu Bong Hahn


"Autoionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference(RPD) method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick"--Abstract, page 2. "The structure in the electron impact ionization cross section in cesium can be partially accounted for by the mechanisms of autoionization and excitation-ionization of 5p-electrons. For electron energies above 17 eV a large fraction of the ions are metastable and can be detected by Auger emission from a metal surface. The experiment was performed in a crossed cesium atom-electron beam apparatus, and the metastable ions were counted with a channel electron multiplier. The metastable ion count rate was a factor of 100 higher than that due to photons from atomic and ionic transitions. We have measured the overall excitation function for a number of Cs⁺ metastable levels, the lowest being 5d{[3 1/2], 3} at 17.02 eV and 5d{[1/2], 1} at 17.06 eV. In addition, by retarding the ions before they reach the Channeltron, the apparatus was made selectively sensitive to vuv photons. The lowest ionic level excited was 5p⁵6s{[1 1/2], 1}, resulting in photon emission at 926.75 Å"--Abstract, page 32. "The gain and total count rate of electron channel multipliers depend strongly on applied magnetic fields. We report experimental results for Channeltrons operated in magnetic fields of up to 300 Gauss, and find that the applied voltage must be increased to about 4000 volts to maintain a sufficiently high gain. Slightly higher count rates are observed if the magnetic field is parallel to the plane of the Channeltron, as compared to perpendicular to that plane"--Abstract, page 65.


Nygaard, Kaare J.

Committee Member(s)

Snow, William R.
Dowell, Jerry T.
Tefft, Wayne E., 1929-1973
Levine, Norman E.



Degree Name

Ph. D. in Physics


University of Missouri--Rolla

Publication Date


Journal article titles appearing in thesis/dissertation

  • Electron impact excitation of autoionizing levels in cesium
  • Excitation of 5p-electrons in cesium by electron impact
  • Channeltron gain in magnetic fields


viii, 79 pages

Note about bibliography

Includes bibliographical references.


© 1972 Yu Bong Hahn, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Electron impact ionization
Photoelectric multipliers

Thesis Number

T 2745

Print OCLC #


Electronic OCLC #


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Physics Commons