Doctoral Dissertations


"An expansion type cloud chamber was used to measure the nucleation rate of water vapor in an atmosphere of helium and argon. A careful study was made of the thermodynamic characteristics during the expansion so that the nucleation data could be interpreted with reasonable accuracy and consistency. A fine wire thermocouple was used to measure the gas temperature during the course of an isentropic expansion in the dry chamber. When the finite heat capacity of the thermocouple is accounted for, it is found that there is almost perfect agreement with the temperature calculated from the equation of state and the pressure measurement. This establishes the expansion cloud chamber as the instrument with the most accurately known thermodynamic characteristics and the one where the supersaturation may be calculated with the greatest precision. The homogeneous nucleation rate of water vapor in a helium atmosphere was measured as a function of temperature, supersaturation and sensitive time. It was found that there exists a form of heterogeneous nucleation occurring above the ion limit at about the critical super-saturation predicted by the classical Becker-Doring theory for homogeneous nucleation. This form of heterogeneous nucleation appears to occur upon chemically bonded centers whose concentration is very low and depends upon the vapor pressure before the expansion. The consistency of the number of the nucleating centers indicates that they may be a neutral product of the action of natural radioactivity and cosmic rays. A semiphenomenological theory was developed along the lines of the classical theory but which includes the chemical bond energy of the heterogeneous nucleating center. The theory predicts a different temperature dependence for the heterogeneous and homogeneous nucleation rates and at least qualitatively explains the essential features of the experimental data. A considerable disparity in the temperature dependence of the critical supersaturation limit has existed for many years. The variation in the temperature dependence with nucleation rate as determined by the author's data shows: (a) that a large part of the disparity is due mainly to the interpretation of the experiments and (b) that the different temperature dependence of the heterogeneous and homogeneous nucleation rates is responsible for the different temperature dependences reported by the various experimenters. It was definite established that the nucleation rate of water vapor is higher in an argon atmosphere than in a helium atmosphere. This may be due to a disruption factor related to the higher velocity of the light helium atoms. It is, however, more likely due to the hydration of the argon atom into the critical cluster with a resultant increased stability in the critical clusters"--Abstract, page ii-iii.


Kassner, James L.

Committee Member(s)

Darkow, Grant L.
Antle, Charles E.
McFarland, Charles E.
Rivers, Jack L.
Lund, Louis H., 1919-1998
Hopkins, Don C.



Degree Name

Ph. D. in Physics


National Science Foundation (U.S.)
United States. Department of Health, Education, and Welfare


University of Missouri at Rolla

Publication Date



xiii, 195 pages

Note about bibliography

Includes bibliographical references (pages 122-126).


© 1968 Louis Benton Allen, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Nucleation -- Mathematical models
Water vapor, Atmospheric

Thesis Number

T 2111

Print OCLC #


Electronic OCLC #


Included in

Physics Commons