As neutrons pass through matter, they make occasional elastic collisions with nuclei. 当中子穿过物质时，偶而与核发生弹性碰撞。
Additional insight is gained by examining the elastic collision of equally massive particles in the center-of-mass frame of reference. 对质量相等的两质点的弹性碰撞更彻底的理解，可通过质心参照系而获得。
