Determination of ultratrace uranium and thorium in high purity aluminium by NAA

Abstract

Ultratrace amounts of uranium and thorium in high purity aluminium were determined by radiochemical neutron activation analysis (RNAA). The aluminium plate samples (ca. 1 ~10 g) were irradiated by thermal neutron flux of 4X 1012 n cm-2 s 1 for 5~10 h at Musashi Institute of Technology Research Reactor (MITRR). After several days the irradiated samples were dissolved in 9 M HC1 for anion exchange chromatography. 239Np and 233Pa adsorbed on the anion exchange resin from 9 M HC1 were selectively eluted with 9 M HC1~5 M HF solution. By the addition of LaCl3 solution to this eluate, 239Np and 233Pa coprecipitated LaF3. ᵞ-Rays from the coprecipitate on a filter paper were measured for determination of uranium and thorium. Several ppt levels of uranium and thorium were able to be determined by this method. Before RNAA the samples were analyzed by INAA to evaluate analytical accuracy of the RNAA method. Influence of sample weight to geometric counting efficiency was corrected in the calculation of radioactivities of 239Np and 233Pa from ᵞ-counting data. The analytical results obtained by RNAA indicated excellent agreement with the INAA results. © 1993, The Japan Society for Analytical Chemistry. All rights reserved.