Preparation of calibrated reference sources containing "fresh" fission products

Abstract

NPL was recently asked to provide reference sources containing g-ray emitting fission product radionuclides, with certification completed within 50 days of the irradiation. Furthermore, the reference sources were to contain fission products, but no fissile material. The samples in the first reference source were to contain a mixture of fission products with only the 235U removed, leaving the fission products as 'undisturbed' as possible. A number of radionuclides were reported in this sample and included: 91Y, 95Zr, 95mNb, 95gNb, 99Mo, 99mTc, 103Ru, 106Ru, 127Sb, 129mTe, 129gTe, 131I,132Te, 132I, 137Cs, 140Ba, 140La, 141Ce, 144Ce, and147Nd. Of these nuclides, NPL provided certified values for 91Y, 95Zr, 95mNb, 95gNb, 99Mo, 99mTc, 103Ru, 106Ru, 132Te, 132I, 137Cs, 140Ba, 140La, 141Ce, 144Ce, and 147Nd. The second reference source focused on a smaller subset of radionulides: 95Zr, 99Mo, 103Ru, 106Ru, 140Ba, and 155Eu, although 95gNb, 99mTc, 132I and 140La were present as daughter radionuclides and 91Y, 127Sb, 129mTe, 129gTe, 131I, 132Te, 137Cs, 152Eu and 154Eu were present as impurities. This paper describes the preparation of these sources, based on a combination of cation- and anion-exchange chromatography with selective precipitation. The separation techniques were used to (1) produce the 'fresh' fission product mixture from irradiated 235U, and (2) isolate the specific set of radionuclides in the second exercise from mixtures containing irradiated 235U and fission products. To enable accurate assay of parent-daughter systems, integrated ingrowth and decay equations were derived from original Bateman equations and tested by observing the 140Ba-140La system over time.