Document Type

Thesis - Open Access

Award Date

1954

Degree Name

Master of Science (MS)

Department

Physics

Abstract

There are many types of detectors of radioactive rays, such as Geiger Counters, ionization chambers, photographic emulsions, electroscopes, and cloud chambers. Many of these give only information such as the amount of radiation or the minimum energy of the rays because the information is registered as a change in voltage or a “count”. Outstanding among the different kinds of detectors is the type commonly called “cloud chambers”. In a cloud chamber the path of the ray* can actually be seen and photographed, its radius of curvature in an electric or magnetic field can be measured, the amount of ionization can be measured by counting the number of ions per length of path, and the amount of deviation from the predicted normal path can be studied. From this type of information the mass, velocity, and charge of the ray can be determined. The basic principle utilized in any chamber is that a gas which is supersaturated with a vapor will act as a means of detection of radioactive rays by forming a cloud trail along the path of the ray. The most common method of obtaining a gas which is supersaturated with a vapor is by cooling. Gas which has been saturated with vapor can be cooled until a high degree of supersaturation is reached if there are no particles in it to act as nuclei around which droplets can form. J.Aitken during his investigations (about 1880) indicated that dust particles do act as such nuclei and utilized the fact to count dust particles. In 1896 C.T.R. Wilson showed that ions formed in a supersaturated gas could also act as centers of condensation. This fact led Wilson to the discovery of his famous “expansion” cloud chamber. It is theorized that high energy rays in their motion through matter ionize many atoms along their path. These ions form nuclei for condensation, thus producing a trail of droplets which are visible to the eye and which also can be photographed if desired. The method used by Wilson for obtaining the supersaturated gas is expansion of a saturated gas by means of piston on the floor of the chamber. This sudden increase of volume causes a decrease of temperature, thus causing the gas to become supersaturated. The main disadvantage in Wilson’s chamber is that it will show tracks for only a very short period of time after expansion and then must be recycled for the next expansion. Therefore, there has been considerable interest in some kind of chamber that would be continuously sensitive. The first continuously sensitive cloud chamber was reported by L.G. Hoxton in 1933. This cloud chamber operated by passing air over water at 70C and thence into a water-jacketed observing channel at room temperature. Condensation phenomena were produced by electric discharges but not by radiation, so this method was not satisfactory. In 1936 R. E. Vollrath described a continuous cloud chamber that operated by interdiffusion of two vapors such as hydrochloric acid vapor and water vapor, at the interface of which the gas became supersaturated with respect to the mixture (dilute hydrochloric acid). A.Langsdorf, Jr. reported progress on a continuous diffusion cloud chamber in 1936. The construction of Langsdorf’s chamber is essentially a glass cylinder with a refrigerated floor and a heated roof. Through the roof the vapor of a liquid with a high vapor pressure is allowed to diffuse and saturate the gas in the chamber. Then as the saturated gas diffuses downward it becomes cooled and thus supersaturated and within a limited region acts as an ion detector. Although diffusion chambers have the advantage of being continuous, they frequently have the disadvantage of having diffuse, fuzzy, or distorted tracks which do not generally present a great problem in a well-designed Wilson expansion chamber. There is a definite need to find out more about the conditions that exist in diffusion chambers in order to improve their design. The purpose of this paper is to investigate some of the conditions that exist in a diffusion chamber, similar to the type proposed by Langsdorf.

Library of Congress Subject Headings

Cloud chamber

Description

Includes bibliographical references

Format

pdf

Number of Pages

34

Publisher

South Dakota State University

Rights

No Copyright - Non-Commercial Use Only
http://rightsstatements.org/vocab/NoC-NC/1.0/

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