Determination of sodium in high-purity zinc and selenium by neutron activation

Abstract

A method is described for the determination of traces of sodium in high-purity zinc and selenium by neutron activation. The sample and portions of standard solution were irradiated in JRR-2 for 20 min at a thermal neutron flux of about 7 × 10¹³n/cm²· sec.The samples irradiated were cooled for about 2 hours.The zinc sample was etched with 5 N sulfuric acid and then dissolved in concentrated hydrochloric acid. The selenium sample was etched with aqua regia, dissolved in concentrated nitric acid, and converted to concentrated hydrochloric acid solution. The sample solution was poured into a hydrated antimony pentoxide (HAP) column (5φ × 30 mm) which was previously conditioned with concentrated hydrochloric acid. The column was washed with concentrated hydrochloric acid. Sodium-24 was adsorbed on HAP but zinc and selenium were not. The column was transferred to a polyethylene vial and its γ-activity was measured with a 3 x 3 inch NaI(Tl) detector and 400 channel pulse-height analyzer. The 2.754 MeV γ-ray photopeak of ²⁴Na was used for the determination. The standard solutions were treated in the same way as the samples. Nuclides produced from zinc and selenium did not interfere with the determination of sodium.
The proposed method was successfully applied to three NBS standard samples. A detection limit of this method was 10^-3 ppm Na in zinc and selenium.