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Proefschrift--Utrecht. / Summary in English, French and German. "Litteratuur": p. 92.

Proefschrift--Utrecht. / Summary in English, French and German. "Litteratuur": p. 92.

Thesis--Wisconsin. / Includes bibliographical references (leaves 110-114).

The present status of the Bethe-Heitler theory of pair production is analysed, and results are given which can be compared with experiment. The main points of interest in the pair formation process are the cross-section, energy and angular distribution of the electrons, the momentum imparted to the nucleus, and the manner in which these factors vary with photon energy and atomic number. Although the assumptions involved, such as the Born Approximation, appear to be justified, a review of the literature shows that experimental results have not always been in entire agreement with theory. For instance, the experimental distribution of Ē₊-Ē₋ follows neither the Bethe-Heitler nor the Jaeger-Hulme theory. The proposed experiment is to be carried out with a cloud chamber using Xenon as the gas, and ThC" as the γ-ray source. The errors involved in the method are discussed. To minimize scattering error a new method of analysis of cloud chamber tracks is suggested, in which the angle between successive equidistant chords is measured. The nine inch chamber is of the rubber diaphragm type. The operation of the chamber and camera has been made entirely automatic. The magnetic field is obtained by a pair of Helmholz coils. Two General Electric F.T. 126 flash lamps provide sufficient light for photography. Stereoscopic pictures are obtained by the double mirror method. A great number of difficulties had to be overcome, especially in the functioning of the expansion valves, in order to get good electron tracks and consistent operation. It has been found that it is very important to use correct procedure in filling the chamber and "cleaning" it out for the production of tracks. Very nice electron tracks have been obtained with a ThC" source and Argon in the chamber. Preliminary observations indicate that the source may need to be shuttered, and that the chamber will need a thin window. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The primary object of this research project has been to construct a Wilson cloud chamber for nuclear physics investigations, in particular, suitable for use with the high voltage Van de Graeff generator now being erected in the Physics Department of the University of British Columbia. The chamber design is based on drawings obtained from the Chalk River Laboratories of the National Research Council, and is basically similar to the design developed by various people through the period 1935 - 1940 at the Cavendish Laboratory, Cambridge. The control unit design is essentially the same as that developed at the Chalk River Laboratories, N. R. C., and provides for automatic operation of the chamber. The whole unit has been assembled on a movable trolley so that the chamber may be used in conjunction with the ion beam from the electrostatic generator. The whole of the machine and assembly work was carried out in the Physics Department at U. B. C., using castings obtained from a local Vancouver firm. It was intended had time permitted to check carefully the performance of the chamber by conducting a brief experiment involving the photographing of numerous electron tracks. To this end a source of Zinc⁶⁵ was obtained, which is a positron emmitter, but only a very preliminary examination of the radiations from it has so far been possible. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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