“…The atom ratio of 240 Pu/ 239 Pu has become an important factor in investigating the source and migration processes of plutonium in the environment [11]. Accelerator mass spectrometry (AMS) is an effective and robust technique for studying long-lived actinides (e.g., 236 U, 237 Np, 239 Pu, and 240 Pu) [12,13,14], and inductively coupled plasma mass spectrometry (ICP-MS) is currently the most widely used technique for measuring actinides because of its lower cost compared to AMS. The distribution, sources, migration, and applications of 137 Cs have attracted extensive attention over the past few decades [15,16,17,18,19,20].…”