This work was supported by the Special Fund for Land and Resources Research in the Public Interest (No.201511046) and the National Natural Science Foundation of China (No.21225314 and No.41102151). We would like to give our gratitude to Zong-yu Chen from IHEG for organizing the field campaign.
Radioactive noble-gas isotopes, SSKr (half-life tl/2=10.8 y), 39Ar (tl/2=269 y), and SlKr (t1/2-229,000 y), are ideal tracers and can be detected by atom trap trace analysis (ATTA), a laser-based technique, fr...