Production and Quality Control of High-Purity Rare-Earth Metal Oxides for Scintillator Crystals of Detecting Medical Systems

Abstract

The positron emission tomography detection device uses scintillator crystals to provide high image quality. Cerium-activated lutetium orthosilicates are promising crystals for PET detectors. The optical properties of the resulting scintillator crystals directly depend on the impurity composition of the starting materials; therefore, rather stringent requirements are set for them: the content of the basic substance Lu₂O₃ is 99.999 wt % and CeO₂ is 99.99 wt %. As a starting material for obtaining lutetium oxide of the required purity, we used its concentrate with a basic substance content of 99.1 wt %, to obtain cerium oxide, REM carbonates containing up to 54% cerium in the composition. The paper presents the schemes of the technological process for obtaining high-purity Lu₂O₃ and CeO₂ based on a combination of methods of extraction and ion exchange. Extraction purification of lutetium and cerium from accompanying rare-earth impurities was carried out using Aliquat 336 and tri-n-butyl phosphate, respectively. In the work, the main modes of operation of the extraction cascades were calculated; the total number of stages for purifying lutetium was 17; for purifying cerium, it was 20. The technology for the purification of lutetium oxide and cerium oxide consists of a combination of purification methods and varying cycles depending on the content of impurities; in this regard, it is necessary to control the quality of the resulting substances practically after each stage. Analytical control of the chemical purity of technological products was carried out by mass spectrometry with inductively coupled and spark sources of sample excitation.