Table Of ContentPURDUE UNIVERSITY
THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION
by______________ Daryl Dale Err et t __________
entitled THE DRIFT VELOCITY OF ELECTRONS IN GASES
COMPLIES WITH THE UNIVERSITY REGULATIONS ON GRADUATION THESES
AND IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS
FOR THE DEGREE OF DOOtOP Of PhllOSOphy
Professor in Charge of Thesis
Head of School or Department
7/
H
TO THE LIBRARIAN:--
1S>
THIS THESIS IS NOT TO BE REGARDED AS CONFIDENTIAL.
PBOFBSSOH IB OHABOB
GRAD. SCHOOL FORM 0
THE DRIFT VELOCITY OF ELECTRONS IN GASES
A Thesis
Submitted to the Faculty
of
Purdue University
by
Daryl Dale Errett
In Partial Fulfillment of the
Requirements for the Degree
of
Doctor of Philosophy
August, 1951
ProQuest Number: 27714299
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PREFACE
It might seem presumptuous to do a thesis on a sub
ject that had long occupied some very great men, but there now
exist greatly improved methods that were not available for
the experimenters of 15 to 30 years ago. After the author
had spent considerable effort on a method he felt to be a
superior one, it appeared possible to resolve some of the
discrepancies existing in the published results of electron
drift velocities in gases, and to resolve these differences
has been one of the objects of this thesis.
Electron drift velocity measurements have been done
primarily by three large groups of people. The first was
the school that did work in close connection with J. 3.
Townsend and V. A. Bailey. The second group was led by
Professor Leonard Loeb. Between these two groups there was
little cooperation, and in the publications of Townsend’s
group the results of Loeb’s workers are all but forgotten»
A third group of people carried out experiments in our
government laboratories during World War II.
The methods and results of these respective groups
can be found in books written by Healey and Reed1, Loeb2, and
Rossi and Staub3. These volumes are considered as general
references for this thesis. Even though the books deal with
ii
some of the same subjects, there is little consistency in
matters of notation. In reading from more than one of these
it is easy to become annoyed with the differences. In this
thesis the author has attempted to define quantities when
they are first introduced, and has endeavored to minimize
the confusion.
The author wishes to express his thanks to Dr. F. F.
Rieke whose guidance and helpful suggestions are deeply ap
preciated. Dr. K. W. Meissner has given aid in the problems
of gas purification, and has kindly allowed the use of instru
ments from his spectroscopy laboratories. Grateful acknowledg
ment is made of the support given by the Physics Department,
the 0. N. R., and A. E. 0.
ill
TABLE OF CONTENTS
Page
ABSTRACT............................................. vii
I. INTRODUCTION.................................... 1
(1) Historical "Notes........................... 1
(2) Methods for Measuring Electron Drfit Velocity. 3
II. THEORY........................................ IQ
(1) Computation of Electron Drift Velocity....... 10
(2) Electron Speed Distributions................ 12
(3) Drift Velocity Calculations Using Average
Values........ 14
(4) Properties of Cas Mixtures......... 17
(5) Graphical Solution of W(E/p)................ 18
III. METHOD, APPARATUS, AND TECHNIQUES............. 20
(1) General Objectives .................... 20
(2) Design Considerations....................... 20
(3) Errors Introduced by Diffusion, Space Charge
and Transient Electron Speed Distributions.... 33
(4) Experimental Techniques..................... 42
IV. RESULTS....................................... 45
(1) Pure Oases,................ 45
(2) Cas Mixtures........ 58
(3) Computations for Cas Mixtures............... 65
V. SUMMARY........................................ 71
APPENDIX A. COMMENTS ABOUT OTHER CAS PROPERTIES....... 74
SELECTED BIBLIOGRAPHY................................. 78
VITA................................................. 81
iv
6'
LIST OF FIGURES AND TABLES
List of Figures
Figure Page
1. Magnetic Deflection Method....................... 4
2. Electrical Shutter Method......................... 5
3. Pulse System of Herr eng.......................... 6
4. Nomograph for Solution of ,V(E/p)................. 19
5. Block Diagram of Circuits........................ 22
6. Photograph of High Voltage Terminal and Column..... 23
7. Photograph of Electron Gun and Puiser............ 24
8. Ionization Chamber and Gas System................ 28
9. Photograph of Ionization Chamber and Preamplifier.. 29
10. Photograph of Gas Purification System............ 30
11. Preamplifier Circuit................... 32
12. Current Pulses for Infinite Planes.. ............ 35
13. Actual Current Pulse............................ 35
14. Charge Density in Ionization Chamber............. 36
15. Diffusion of Charge Distribution................ 37
16. Effect of Diffusion and Correction............... 38
17. Oscilloscope Traces Showing Delayed Electron
Emission in Argon.............................. . 75
List of Tables
Table Page
I. Comparison of Pulse Methods..................... 9
II. Computed Mean Decay Time......................... 42
v
LIST OP GRAPHS
Graph Page
1. Drift Velocity of Electrons in Argon (E/p 0-20).*.. 46
2. Drift Velocity of Electrons in Argon (E/p 0-4).... 47
3. Drift Velocity of Electrons in Helium (E/p 0-10)... 49
4. Drift Velocity of Electrons in Helium (E/p 0-4).... 50
5. Drift Velocity of Electrons in Hydrogen........... 51
3. Drift Velocity of Electrons in Nitrogen (E/p 0-20). 53
7. Drift Velocity of Electrons in Nitrogen (E/p 0-2).. 54
8. Drift Velocity of Electrons in Carbon Dioxide..... 56
9. Drift Velocity of Electrons in Water Vapor........ 57
10. Drift Velocity of Electrons in A-Hg Mixtures...... 59
11. Drift Velocity of Electrons in A-Ng Mixtures...... 61
12. Drift Velocity of Electrons in A-COo Mixtures
(E/p 0-10).................. 62
13. Drift Velocity of Electrons in A-CO Mixtures
(E/p 0-2)....................................... 63
14. Drift Velocity of Electrons in A-HgO Mixtures..... 64
15* Drift Velocity of Electrons in Ng-HgO Mixtures 66
13. h(u) for Argon-Nitrogen Mixtures................. 68
17. \(u) for Argon-Ni trogen Mixtures................. 69
18. Computed and Measured Drift Velocities in A-Ng 70
vi
ABSTRACT
The drift velocities of free electrons have been
measured in pure argon, helium, hydrogen, nitrogen, carbon
dioxide, and water vapor, and in 22 different mixtures of
these gases by use of a pulse technique. By use of electronic
pulse circuits and an accurately constructed ionization
chamber, it has been possible to determine electron drift
velocities more easily and more accurately than had been
done with previous methods.
fractional-microsecond pulses of 150 Kev electrons
enter one end of an ionization chamber through a metal foil.
These electrons create dense bursts of ionization, and an
electric field maintained within the chamber causes the free
electrons to drift to a collecting electrode. The chamber is
15.6 cm long and has potential distributing rings within it
to ensure a homogeneous axial field. The current to the
collecting electrode (caused by the electron drift) is amp
lified and displayed on an oscilloscope having a driven sweep,
and the drift time is measured by use of calibrated time
markers. To assure high gas purity, a purification system
was connected to the chamber; the gases were investigated
for impurities by spectroscopic means.
The drift velocities of electrons in argon found here
disagree with the recent results of Klema and Allen, whereas
results of Nielsen and of Herreng were only slightly higher
vii
