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

• Published in: Vacuum 2025-01, Vol.231, p.113778, Article 113778
• Main Authors: Liu, Kejing, Jie, Wanqi, Kang, Zhe, Liu, Jinbo, Zhang, Xianggang, Guo, Shixuan, Cai, Zhuochen, Zheng, Dan, Yin, Ziang, Zhao, Qinghua, Luo, Fa, Xiong, Shitao, Wang, Shusheng, He, Xuxin, Yue, Aizhong, Wang, Tao
• Format: Article
• Language: English
• Subjects: 227Ac separation; LaBr3:Ce3; Low-background; Vacuum distillation
• ISSN: 0042-207X
• DOI: 10.1016/j.vacuum.2024.113778

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. •Vacuum distillation for separating 227Ac from raw LaBr3 was firstly achieved by theory and experiment.•One-step distillation successfully reduced 227Ac to 50%–40 %, obtaining low background LaBr3:Ce3+ crystals.•Optimal process conditions for vacuum distillation to separate 227Ac from LaBr3 were established.•The optimization of impurity significantly improves light yield and energy resolution of LaBr3:Ce3+ crystal.