问题 选择题

某原子核A经过一次β衰变变成B核,B核再发生一次α衰变变成C核,则( )

A.核A的中子数减核C的中子数等于2

B.核A的质量数减核C的质量数等于5

C.原子核为A的中性原子中的电子数比原子核为B的中性原子中的电子数多1

D.核C的质子数比核A的质子数减少1

答案

答案:D

题目分析:根据原子核经过一次,电荷数减小2,质量数减小4,一次β衰变后电荷数增加1,质量数不变,进行分析即可.

解:设原子核A电荷数为x,质量数为y,中子数为:y-x

原子核经过一次α衰变,电荷数减小2,质量数减小4,一次β衰变后电荷数增加1,质量数不变:

则:发生β衰变后变成的原子核B的电荷数为:x+1,质量数为:y,中子数为:y-x-1

原子核B发生α衰变后变成的原子核C的电荷数为:x+1-2=x-1,质量数为:y-4,中子数为:y-4-x+1=y-x-3

A:核A的中子数比核C的中子数多:(y-x)-(y-x-3)=3,故A错误.

B:核A的质量数比核C的质量数多:y-(y-4)=4,故B错误.

C:原子核A的中性原子中的电子数比原子核B的中性原子中的电子数多:x-(x+1)=-1,即少一个,故C错误.

D:核C的质子数比核A的质子数少:x-(x-1)=1,故D正确.

故选:D

点评:明确α衰变,β衰变的实质,分别表示出ABC三个原子的电荷数,质量数,中子数进行比较即可.

材料题
阅读理解

阅读理解

     Many of us already know about several American superstitions(迷信). Having a black cat cross your

path, walking under a ladder, and breaking a mirror are all bad luck. In addition, there are many other

superstitions that are worth knowing. Understanding them will keep you safe from evil spirits -if you believe

in such things -and impress your American friends when you mention them.

     Like the superstitions in other cultures, American superstitions often involve the things important in daily

life, such as health, numbers, and marriage. For example, have you ever had a cough that would not go

away? According to one American superstition, you should take a piece of your hair and put it between

two slices of buttered bread. Next, feed this hair sandwich to a dog and say, "Eat well, you hound, may

you be sick and I be sound." This will trick the evil spirits and help your cough. It will also raise some

eyebrows if you try it.

     In American superstitions, the number three is very important. Often, Americas will say, "All things

come in threes." Three is lucky because it represents the traditional family: mother, father, and child.

Therefore, gifts, letters, and guests will often arrive at your home in groups of three. However, it is also

possible for bad events, like accidents and funerals, to come in threes as well.

     Another time people pay attention to superstitions is when they get married. During a wedding, brides

must wear or carry "something old, something new, something borrowed, and something blue". The old

and borrowed things will bring luck to the person who gives them to the bride. The new and blue things

will bring good fortune to the bride herself. The next time someone you know is getting married, be sure to

recite this phrase.

     As it would be unlucky to discuss one more superstition, we will wind things up here. Keep your fingers

crossed, and stay lucky!

1. The passage is most probably entitled _____.       

A. American's Bad Luck

B. Cross-culture and Superstitions

C. American Superstitions

D. Daily Life in Superstitions

2. The underlined sentence in the second paragraph "It will also raise some eyebrows if you try it."

means _____.       .

A. when you try it, the dog will raise its eyebrows.

B. you will make people surprised when you try this trick

C. only if you raise your eyebrows can the trick work

D. you will believe in the trick after you try it

3. In American's view, the number three is a(n) _____ number.

A. lucky

B. unlucky

C. special

D. ordinary

4. On the wedding, the bride often uses old and borrowed things so as to _____.         .

A. save some money for the wedding

B. bring good luck to the people who give them to the bride

C. give the good luck to the bride herself

D. pass the bad luck to others

5. After reading the passage, we may feel it is written in a _____ tone.

A. formal

B. serious

C. humorous

D. critical