在匀强磁场中有一个静止放置的放射性元素的原子核，当它放出一个_爱下问搜题

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问题问答题

在匀强磁场中有一个静止放置的放射性元素的原子核，当它放出一个α粒子后，它们的速度方向都与磁场方向垂直.若测得α粒子和反冲核的轨道半径之比为44∶1，如图所示.则反冲核的电荷数是多少？

答案

88

放射性元素的原子核，放出α粒子的过程动量守恒，由于初始动量为零，所以末态动量也为零，即α粒子和反冲核的动量大小相等、方向相反，即p₁=p₂=p.因为它们在磁场中均做匀速圆周运动，故：

,,所以α粒子的半径：

设反冲核的电荷量为Q，则反冲核的半径：

所以：,Q=88e.

完形填空

Granny Sarya lived outside Moscow． Her only son  16  to Afghanistan(阿富汗) and was killed in action there．Soon after that, her husband lost his job． The old man was always   17  food and clothes．And on a winter night he went out alone when Sarya was asleep． The next morning he was   18  dead in a cold lake． And his worn-out coat was   19  in a tree not far away． Sarya was so   20  that she nearly took her own life．
Things got worse and worse after that． She always lived in hunger and cold． She had hoped that the government(政府) could help her but she    21 ．
It was a cold windy night． The old woman couldn't   22 asleep at all． She had to get up． She decided to write a letter to God（神）, asking for  23 ． She wished God to give her 100 rubles (卢布), so she could buy some food for herself． When she  24 writing it, she found she had no  25 ． She had to put the  26  at a crossing．   27  the next morning a policeman found the letter． He read it to his comrades．They were all so   28  that they gathered some rubles and sent them to the poor old woman．
At first Granny Sarya was happy． But after she   29  the money, she became   30  and said, “I'm told that all things that are touched by the policeman will be only a half left!”

A．worried about

B．pleased with

C．thinking about

D．Wonderfully

单项选择题

禁灸穴是

A．石门
B．睛明
C．神厥
D．乳中
E．囟会