题目内容
处于静止状态的某原子核X,发生α衰变后变成质量为M的原子核Y,被释放的α粒子垂直射人磁感强度为B的匀强磁场中,测得其圆周运动的半径为r,设α粒子质量为m,质子的电量为e,试求:
(1)衰变后α粒子的速率
和动能Eka;
(2)衰变后Y核的速率
和动能Eky;
(3)衰变前X核的质量Mx.
(1)衰变后α粒子的速率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319153203.gif)
(2)衰变后Y核的速率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319169202.gif)
(3)衰变前X核的质量Mx.
(1)
,
,(2)
,(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319231893.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319185449.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319200500.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319216694.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319231893.gif)
(1)α粒子在匀强磁场中做圆周与运动所需的向心力同洛仑兹力提供,
即
,
粒子的带电量为q=2e (2分)
所以α粒子的速率:
, 动能:
(2分)
(2)由动量守恒
, (2分)
所以
(2分)
(3)由质能方程:
,而
, (2分)
所以
(2分)
衰变前X核的质量:
(2分)
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319247554.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319263201.gif)
所以α粒子的速率:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319278517.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319294694.gif)
(2)由动量守恒
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319309511.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153193251023.gif)
(3)由质能方程:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319341457.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319419488.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115319434816.gif)
衰变前X核的质量:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153194501388.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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