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Absorption and scattering of radium gamma radiation in water Smocovitis, Dimitrios

Abstract

The first part of this thesis describes measurements made with medical radium sources to determine the ratio of the exposure in a large (essentially infinite) water "phantom" to the exposure at the same point in air, i.e., to determine the fractional transmission in an "infinite" water phantom. The fractional transmission was measured as a function of the distance between the radium sources and the measuring instrument. The radium used was sealed in platinum containers which absorbed the primary alpha and beta rays from the radium so that the exposures were due to gamma rays only. All measurements were made with small air-filled ionization chambers with plexiglass walls. Ionization currents were measured with these chambers in water and in air. The corrections which were required to determine the ratio of exposure in water to exposure in air from these measurements and the preliminary experiments necessary to determine the required corrections are described in the thesis. The fractional transmission through water is shown graphically as a function of the distance between source and point of measurement. Also, the relationship is described by an empirical equation. The curve drawn fits the experimental points obtained under a variety of conditions of measurement within the experimental error of 1/2 to 1%. The second part of the thesis describes measurements of ionization currents made with an experimental set-up in which the ionization chamber was at a fixed distance vertically below the radium and the whole assembly was moved relative to the surface of a water phantom. From measurements made with the radium above the surface, in the surface and below the surface of the water, it was possible (a) to obtain data which could be compared with the results of Part I and (b) to obtain correction factors which could be applied to the results of Part I to correct for reduced scatter when the radium was in the surface, rather than well immersed in water. The results of the present experiment are compared with those of previous workers.

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