Separation of radioactive isotope 227Ac from LaBr3 via vacuum evaporation for low-background scintillating detectors

Abstract

Both radioactive isotopes ¹³⁸La and ²²⁷Ac in LaBr₃:Ce crystal typically produce considerable intrinsic background signals, and thus hinder their applications with low count rates. Since the complete separation of ¹³⁸La is almost impossible, the contamination of ¹³⁸La is stubbornly present in all La-halide based scintillators. In this study, an efficient purification protocol based on vacuum distillation was developed to separate ²²⁷Ac from feedstock and reduce intrinsic background signal at 1.6–3 MeV introduced by ²²⁷Ac in LaBr₃:Ce crystals. Through combined theoretical and experimental analysis, the alpha contamination from ²²⁷Ac in LaBr₃: Ce was reduced exploiting the different evaporation behaviors of LaBr₃ and AcBr₃. Additional impurities were also reduced to lower levels, as confirmed by glow discharge mass spectrometry (GDMS). The purified material, distilled at various temperatures (1203 K, 1253 K, and 1303 K), was used to grow LaBr₃:Ce single crystals for performance evaluation. The crystals distilled at 1203 K demonstrated enhanced scintillation performance, featuring lower background counts (0.0181 counts·s⁻¹·cm⁻³ @1.6–3 MeV) by approximately 50%–60 % of untreated sample and excellent energy resolution (2.47 %@662 KeV). This study presents an effective approach for preparing low-background lanthanum bromide, so as to offer valuable insights for isotope separation in scintillation crystals by vacuum distillation.