The abundance of those lighter elements allowed scientists to deduce that fission reactions must have gone on for hundreds of thousands of years 这些较轻元素的含量让科学家推论出，核分裂反应必定进行了好几十万年。
2.
Fast - moving neutrons are produced by fission reaction in a nuclear reactor . water is commonly used to moderate and control the speed of neutrons 核电站的核反应堆中，核裂变会产生高速移动的中子，通常是用水去阻隔及控制中子的移动速度。
3.
Fast - moving neutrons are produced by fission reaction in a nuclear reactor . water is commonly used to moderate and control the speed of neutrons 核电站的核反应堆中，核裂变会产生高速移动的中子，通常是用水去阻隔及控制中子的移动速度。
