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The effects of 50 kilovolt x-rays on the alkali metal borohydrides Walker, Leonard George

Abstract

The marked physical changes in potassium boro-hydride such as decrepitation and the development of a deep blue coloration when the solid compound is exposed to ionizing radiation stimulated a study of the effects of 50 Kvp X-rays on the alkali metal borohydrides to determine the nature of the radiation induced changes such as color center formation and chemical decomposition. Methods were developed to prepare the alkali metal borohydrides in a form suitable for radiation studies. Solvents studies showed that anhydrous hydrazine was an exceptionally good solvent for potassium borohydride, the solubility being 28.3 grams KBH₄ per 100 grams at 18.5° C. The handling of hydrazine as a solvent required the construction of special apparatus. A study of the use of hydrazine as a solvent for other ionic borohydrides and/or the growth of crystals suitable for spectroscopic work is incomplete. Therefore, the spectroscopic studies on radiation induced absorption bands was done mainly with thin pressed pellets. The borohydrides of rubidium and cesium were prepared by metathesis reactions from potassium borohydride via a sulfonium borohydride. The preparation of the previously unreported trimethylsulfonium borohydride is described. Color center formation was studied by spectroscopic methods only and the F and U type centers have been tentatively identified. The thermal stability and optical bleachability of some of the radiation induced absorption bands were examined. Chemical studies of radiation damage in potassium borohydride failed to show the presence of free alkali metal. Gaseous boron hydrides were also undetectable. Mass spectrometric examination of gaseous material evolved during irradiation showed only hydrogen to be present. No gas was evolved when heavily irradiated samples of potassium borohydride were dissolved in liquid ammonia. A discussion of methods and apparatus characteristic to the radiation studies such as the X-ray generator, radiation vessels, vacuum system, and a section on radiation dosimetry is included in the thesis. The intensity of X-rays generated by the Machlett OEG-60 X-ray tube was determined by the application of the included dosimetry data together with a calorimetric measurement of the output flux of the tube. At 50 Kvp and 28 milliamperes the intensity output was found to be 0.220 cal.min.⁻¹ cm.⁻² at the tube port. Some suggestions for further work are outlined at the end of the study.

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