题目内容
(9分)在可控核反应堆中需要给快中子减速,轻水、重水和石墨等常用作减速剂。中子在重水中可与
核碰撞减速,在石墨中与
核碰撞减速。上述碰撞可简化为弹性碰撞模型。某反应堆中快中子与静止的靶核发生对心正碰,通过计算说明,仅从一次碰撞考虑,用重水和石墨作减速剂,哪种减速效果更好?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914235347.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914344440.png)
重水减速效果更好
试题分析:设中子质量为mn靶核质量为m,
由动量守恒定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914515722.png)
由能量守恒定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519145781048.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914656159.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914781764.png)
在重水中靶核质量:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914843603.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151914921570.png)
在石墨中靶核质量:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151915046602.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151915171607.png)
与重水靶核碰后中子速度较小,故重水减速效果更好。
点评:学生知道在弹性碰撞中,两物体动量和能量都守恒,在非弹性碰撞中,只有动量守恒,能量不守恒。
![](http://thumb2018.1010pic.com/images/loading.gif)
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