Development of gamma spectrometric method for the determination of thorium in phosphoric acid solution

Abstract

Gamma spectrometric determination of thorium in sintered thoria dissolved in strong phosphoric acid was studied using a high purity germanium (HPGe) detector. 232 Th was determined using the highly abundant (27%) gamma ray (911.4 keV) emitted by its daughter 228 Ac. The count rates in peak regions were plotted against the amount of thorium present in thorium nitrate working standard solution to obtain a calibration curve and the extent of thoria dissolved in 88% phosphoric acid was determined. Further studies on determination of thorium were carried out using thorium phosphate solutions, instead of using thorium nitrate working standard solutions. The solution of thorium phosphate obtained after quantitative dissolution of thoria in 88% phosphoric acid was also found to give a linear calibration curve at 911.4 keV. Using the calibration curves, expected count rates for thorium in sintered thoria dissolved in 88% phosphoric acid were calculated and were in good agreement (±3%) with the observed count rates.