Spectrographic Determination of Impurity Calcium in Thorium and Thorium Dioxide with the Transient Discharge Source Unit

概要

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A spectrographic method was studied to determine microamount of calcium in thorium metal and thorium dioxide, and it was found that calcium in thorium could be determined by exciting sample solution in a porous-cup electrode with the transient discharge source unit. The results obtained were as follows : (1) Thorium metal and thorium dioxide could be dissolved in hydrochloric acid by adding a trace of hydrofluoric acid. Taking into account the spectral intensity of calcium, the concentration of thorium solution was adjusted to 10 mg/ml. (2) The discharge conditions were E (discharge voltage)=225V, C=22μF, L =30μH, and R=2Ω. (3) Preliminary discharge was done for 40 sec in order to photograph the spectra emitted for a stable discharge period. (4) The influence of hydrofluoric acid which was added to dissolve sample was examined, and consequently this was avoided by removing hydrofluoric acid immediately after dissolution of the sample. (5) Samples containing 0.024 to 0.3 per cent of calcium were analysed with Sr II 4215.52A/Ca II 3933.67A as the analytical line pair, the reproducibility being about 7 to 9 per cent of the content of calcium. (6) It was ascertained that the lower limit of the determination of calcium could be extended down to about 0.001 per cent by using thorium of higher purity as the base material.
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