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dc.contributor.authorScott, Patricia Barrieen
dc.date.accessioned2018-05-22T12:47:57Z
dc.date.available2018-05-22T12:47:57Z
dc.date.issued1962
dc.identifier.urihttp://hdl.handle.net/1842/30736
dc.description.abstracten
dc.description.abstractThe aim of this thesis was to make a combined theoretical and experimental investigation into the saturation characteristics of two types of parallel plate ionization chambers - the free -air chamber and the extrapolation chamber.en
dc.description.abstractDespite the great importance of free -air chambers in standardising laboratories, little theoretical consideration seems to have been given to their saturation losses. The theories surveyed in 1.2 deal with uniform ionization in a parallel gap and are not directly applicable to a free -air chamber where the X -ray beam often occupies a small proportion of the collecting volume. Hubner (1958) appears to be the first to calculate the recombination occurring in a free -air chamber. He modified the equation of Von Engel and Steenbeck to take into account the fact that the ionization did not fill the space between the electrodes. He claimed that correction factors calculated from his formula agreed within 0.3 per cent with factors determined experimentally at the National Bureau of Standards. We found that these experimental results covered only a limited range of conditions and as they concerned corrections usually less than 1 per cent, hardly constituted an accurate check of the theory.en
dc.description.abstractWe felt that Hi.bner °s treatment could be improved upon by a different choice of recombination formula. Although Shevyrev's work pointed to Mies equation, we decided to use the derivation due to Boag and Wilson which was in a more convenient form for the further modifications we intended to carry out. By considering the effects of space charge and ion diffusion on the basic recombination equation, we sought to derive an expression for the saturation losses in a free -air chamber. We then planned to check our theory by experiments using a free -air chamber (Greening, 1960) over a wide range of operating conditions.en
dc.description.abstractIt was foreseen that it would be a formidable task to set up a theory governing saturation losses in an extrapolation chamber. Loevinger (1953) quoted an empirical relation for f as a function of (1/√Vd) obtained from experiments with ß-ray sources for plate spacings in the range 0.01 to 0.2 cm. and ionization intensities up to 25 e.s.u. /cm.³sec. This function for f is at variance with all previously described theories. We would expect the situation in an extrapolation chamber to be an extremely complex one since the use of very small air gaps and low ß-intensities is likely to result in losses from diffusion and initial recombination superimposed on volume recombination losses. Loevinger's result does, however, seem surprising since all theories describing these types of losses contain V to the power 1 if not higher.en
dc.description.abstractIt seemed worth-while, therefore, to design and construct a simple extrapolation chamber and make an intensive study of the variation of ionization current with the various parameters involved. We planned to discuss the theoretical significance of these experimental results, making quantitative evaluations where possible.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2018 Block 19en
dc.relation.isreferencedbyen
dc.titleA study of the saturation characteristics of ionization chambersen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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