"A long-sensitive time Wilson Cloud Chamber has been built and tested. A usable sensitive time of 2.5 seconds has been achieved by the use of a system of five expansion valves, the first three of which are used to obtain the sensitive time and the final two to continue the expansion at a supersaturation slightly less than critical in order to allow all droplets formed to grow in size and fall into the liquid. This system of continued expansion, coupled with delayed recompression, has been proved to reduce the background density in the chamber to an average operating value of one drop in 20 cm3.
Re-evaporation nuclei have been investigated and evidence has been given supporting their existence as well as their virtual elimination as a source of background in this chamber. The production and existence of photochemical nuclei has been studied, the primary results being that these nuclei are uncharged and that the supersaturation required for condensation depends upon the duration and intensity of ultraviolet irradiation.
Five classes of condensation nuclei were observed in the chamber, each of which present a potential source of chamber background. These are: (1) uncharged aggregates of molecules condensed upon at supersaturations greater than that required for ions, (2) ions formed by high energy particles, (3) field sensitive nuclei produced by the clearing field electrode which are condensed upon at supersaturations less than critical, (4) field-sensitive nuclei condensed upon in the absence of an electric field and requiring less than critical super-saturation, and (5) field-insensitive photo-chemical nuclei which may be condensed upon at most any degree of supersaturation depending upon the period of time and intensity of ultra-violet irradiation.
The low background and long sensitive time mentioned can be achieved easily due to the great versatility in operating conditions afforded by the expansion valve system and the electronic time delay and cycling units"--Abstract.
Kassner, James L.
M.S. in Physics
Missouri School of Mines and Metallurgy
v, 43 pages
© 1958 Donald A. Rinker, All rights reserved.
Thesis - Open Access
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Rinker, Donald A., "A study of background in a long sensitive time Wilson cloud chamber" (1958). Masters Theses. 2553.