Spectrographic Determination of Impurity Ca in Th and ThO₂ with the Transient Discharge Source Unit

Abstract

A spectrographic method was studied to determine microamounts of Ca in Th metal and ThO₂, and it was found that Ca in Th 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) Th metal and ThO₂ could be dissolved in HCl by adding a microamount of HF. Taking into account the spectral intensity of Ca, the concentration of Th solution was adjusted to 10 mg/mL. (2) The discharge conditions were E(discharge voltage)=225 V, C=22 μF, L=30 μH, R=2 Ω. (3) Preliminary discharge was done for 40 sec in order to photograph the spectra emitted in a stable discharge period. (4) The influence of HF which was added to dissolve the sample was examined, and this could be avoided by removing HF immediately after the dissolution of the sample. (5) Samples containing 0.024 to 0.3 per cent of Ca were analysed with Sr II 4215.52 Å/Ca II 3933.67 Å as the analytical line pair, the reproducibility being 7 to 9 per cent of the content of Ca. (6) It was ascertained that the lower limit of the determination of Ca could be depressed down to about 0.001 per cent by using Th of higher purity as the base material.