This thesis is devoted to some aspects of the theory of the weak continuous gamma radiation (often called 'Internal Bremsstrahlung') which accompanies beta processes, i.e. negative and positive electron emission and orbital electron capture. Whenever a beta process is accompanied by this gamma radiation, it will be called a "radiative" beta process, otherwise "radiationless". The results presented in this thesis go beyond those obtained by other authors in two respects. In the first place, the radiative beta emission probability is calculated for an allowed transition taking into account an arbitrary mixture of all the five beta interactions. Previously, only the theory for the case of pure interactions has been carried out. In the calculations, as in previous ones, Coulomb effects have been neglected. In the second place, the radiative K capture probability is calculated for an all owed transition taking into account again an arbitrary mixture of the five beta interactions, and, in addition, Coulomb effects. Previously, only the case of pure interactions with the neglection of Coulomb effects has been considered. In order to take Coulomb effects into account, a "semi-relativistic" approximation for the solutions to the Dirac equation with a Coulomb potential has been developed. It turns out that taking Coulomb effects into account reduces the probability of radiative K capture by an order of magnitude. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A scintillation counter for the measurement of extremely low specific beta activities has been developed which achieves its high sensitivity through the application of large amounts of radioactive substance, and the use of an efficient liquid scintillation phosphor. The counter can be used in two different ways; as a volume counter and as a multiple-sample counter. In the first type of counter the solid radioactive sample is mixed with the liquid phosphor to form a transparent paste; in the second type a smaller amount of solid sample is spread out on a large surface of cellophane and immersed in the scintillating fluid. Experiments have been made with K⁴⁰ , C¹⁴ , and S³⁵ to determine the range of application, sensitivity, and efficiency of the counters. The volume counter can be used to assay a wide variety of material and is especially suited for biological problems. Its sensitivity was found to be better than 10⁻¹¹ curies/gm., while that of the multiple-sample counter is of the order of 10⁻¹⁰ curies/gm.. These sensitivities can be measured with a good degree of reproducibility and are superior to the conventional methods, with the exception of the elaborate screen-wall counter method. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

published_or_final_version / Physics / Master / Master of Science

Thesis (M. Sc.)--University of Hong Kong, 1965. / Mimeographed.

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Thesis (M.Sc.)--University of Hong Kong, 1965. / Also available in print.

Thesis (Ph. D. in Physics)--University of California, Berkeley, Sept. 1958. / Also issued as UCRL-8324. Includes bibliographical references (leaves 85-87).