Efficient Separation of Ar and Kr from Environmental Samples for Trace Radioactive Noble Gas Detection

Abstract

Radioactive noble-gas isotopes, 85 Kr (half-life t 1/2 =10.8 y), 39 Ar (t 1/2 =269 y), and 81 Kr (t 1/2 =229,000 y), are ideal tracers and can be detected by atom trap trace analysis (ATTA), a laser-based technique, from environmental samples like air and groundwater. Prior to ATTA measurements, it is necessary to efficiently extract krypton and argon gases from samples. Using a combination of cryogenic distillation, titanium chemical reaction and gas chromatography, we demonstrate that we can recover both krypton and argon gases from 1−10 L "air-like" samples with yields in excess of 90% and 98%, respectively, which meet well the requirements for ATTA measurements. A group of testing samples are analyzed to verify the performance of the system, including two groundwater samples obtained from north China plain.

Dual Separation of Krypton and Argon from Environmental Samples for Radioisotope Dating

“…To remove the large amounts of hydrogen that can be present for saltwater samples stored in steel containers, a second getter at room temperature was used as proposed in Stout et al Argon recoveries >97% and purities >99% were reached within 2 h of processing time. In Tu et al the purification of the argon fraction was integrated into the krypton purification system by gettering the effluent from the cryogenic distillation with a titanium sponge. For 5–10 L airlike samples, purity and recovery in excess of 90% for krypton and 95% for argon were obtained, tolerating methane admixture up to 1 L. However, the krypton purity which is a key requirement for 81 Kr and 85 Kr analysis particularly for small samples, dropped from 91.8% for 5 L air samples down to 56.2% for 1 L samples, and the time needed for purifying a sample exceeded 5 h. Moreover, the system was not capable of purifying samples with high (>5 L) methane content.…”