Technology for gadolinium-based ultra-low-background compounds. Part 1. Studies of the impurity composition of gadolinium-containing compounds for determination of promising raw materials

Abstract

The purpose of this work was to identify promising raw materials for creating composite materials that effectively capture neutrons in experiments on the study of rare physical processes. Such composites are made on the basis of a polymer matrix impregnated with gadolinium. In this case, the intrinsic radioactive background of the composite, determined primarily by the residual content of uranium and thorium, should be no more than 100 μBq/kg, which, in terms of the concentration in the materials, is no more than 1·10–9 % (wt.) for U and 2,5·10–9 % (wt.) for Th. In the study of ten commercial inorganic gadolinium-containing compounds (oxide, chloride, sulfate, nitrate) using inductively coupled plasma mass spectrometry (ICP-MS), a method was developed for determination of 65 impurity elements with a detection limit of 10–5–10–9 % (wt.) depending on the specific impurity. It is shown that when analyzing gadolinium-containing compounds by the ICP-MS method for the quantitative measurement of concentrations of difficult-to-detect elements, it is recommended to use the following isotopes: 82Se, 147Sm, 151Eu, 163Dy, 178Hf, 188Os, 194Pt. The detection limit for impurities making the greatest contribution to the residual radioactivity was reduced to 1.1·10–9 % (wt.) for U and to 1.6·10–9 % (wt.) for Th. It was found that the content of U and Th depends more on the genesis of the raw materials from which the gadolinium-containing compounds were obtained than on the general chemical purity of the compounds, which varied from 99.45 to 99.9994% (wt.) in the samples under study. The lower content of U and Th is observed in gadolinium-containing compounds obtained from the secondary raw materials (extraction phosphoric acid) or from mineral raw materials formed in sedimentary rocks (phosphogypsum). It is these compounds that should be considered as the most promising raw materials for development of the technology of the gadolinium-based ultralow-background compound, which is used as a neutron-absorbing additive in detectors and structural composite materials.This work was supported by the Ministry of Science and Higher Education of the Russian Federation, unique project identifier RFMEFI60419X0238.