Radiochemical separation of 231Pa from siliceous cake prior to its determination by gamma ray spectrometry

Abstract

Abstract A simple and fast radiochemical method for the separation of protactinium (231Pa) from siliceous cake for its determination by gamma ray spectrometry is described. The method involves (a) a novel approach, the fusion of the siliceous cake with sodium peroxide, (b) the dissolution of the fused mass in nitric acid and (c) the co-precipitation of 231Pa with manganese dioxide formed in-situ by the addition of solid manganous sulfate and potassium permanganate to the solution. The fusion, effected in a single step, is simpler and highly effective in comparison to methods reported hitherto in literature. The radiochemical yield of 231Pa, determined using 311.9 keV gamma ray of 233Pa radiotracer is quantitative (~90%). The decontamination factors calculated using gamma ray spectrometry and energy dispersive X-ray fluorescence measurements show that the separation from the interfering radionuclides is high whereas separation from major and minor elements is good. Separation by ion-exchange method in hydrochloric acid, hydrofluoric acid and oxalic acid media have comparatively much lower yields. The concentration of 231Pa in the siliceous cake measured using interference-free 283.6 keV gamma ray was found to be (6.4±0.33) μg kg−1. The measured concentration of 231Pa was well above the limit of quantitation whereas the coefficient of variation was ~5%. The improvement in the limit of detection was due to the reduction in spectral background. Systematic evaluation of various uncertainty parameters showed that the major contributors to the combined uncertainty were efficiency of the high purity germanium detector and the counting statistics. The present sample decomposition and separation methods are robust, simple to perform and can be effectively used for the determination and hence source prospecting of protactinium.