tracer isotope

例句：

1. 1. The team used tracer to map the underground water flow.
   该团队使用示踪剂来绘制地下水流图。
2. 2.The scientist used tracer isotope to study the movement of atoms.
   科学家使用示踪同位素来研究原子的运动。
3. 3.The researchers found tracer isotope in the riverbed, indicating that the water had been flowing through the area for a long time.
   研究人员在河床发现了示踪同位素，这表明河水已经流经该地区很长时间了。