Production and quality control of high-purity rare-earth metal oxides for scintillator crystals of medical detection systems

The positron emission tomography (PET) detector uses scintillator crystals to provide high image quality. Cerium-activated lutetium orthosilicates are promising crystals for PET detectors. The optical properties of resulting scintillator crystals directly depend on the impurity composition of starting materials, so they are subject to considerably stringent requirements to the basic substance content: Lu₂O₃ – 99.999 wt.%, CeO₂ – 99.99 wt.%. A starting material used for obtaining lutetium oxide of the required purity was its concentrate with a basic substance content of 99.1 wt.% with REM carbonates containing up to 54 % cerium used to obtain cerium oxide. The paper presents process flow diagrams for obtaining high-purity Lu₂O₃ and CeO₂ based on a combination of extraction and ion exchange methods. Extraction purification of lutetium and cerium from accompanying rare-earth impurities was carried out using Aliquat 336 and tri-n-butyl phosphate, respectively. Main operating modes of extraction cascades were calculated. The total number of stages was 17 for lutetium purification, and 20 for cerium purification. The purification technology for lutetium and cerium oxides consists in combining purification methods and varying cycles depending on the content of impurities. In this regard, it is necessary to control the quality of resulting substances practically after each stage. The chemical purity of technology products was subjected to analytical control by mass spectrometry with inductively coupled plasma and a spark excitation source.

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