Question

下列說(shuō)法正確的是（ ）
A．Ra衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_ST/1.png">Rn要經(jīng)過1次α衰變和1次β衰變
B．U衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_ST/3.png">Pa要經(jīng)過1次α衰變和1次β衰變
C．Th衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_ST/5.png">Pb要經(jīng)過6次α衰變和4次β衰變
D．U衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_ST/7.png">Rn要經(jīng)過4次α衰變和4次β衰變

Answer 1

【答案】分析：經(jīng)過α衰變，電荷數(shù)少2，質(zhì)量數(shù)少4，經(jīng)過β衰變，電荷數(shù)多1，質(zhì)量數(shù)不變．根據(jù)該規(guī)律進(jìn)行判斷．
解答：解：A、Ra衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_DA/1.png">Rn，質(zhì)量數(shù)少4，經(jīng)過1次α衰變，電荷數(shù)少2，知發(fā)生0次β衰變．故A錯(cuò)誤．
B、U衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_DA/3.png">Pa，質(zhì)量數(shù)少4，知經(jīng)過1次α衰變，電荷數(shù)少1，知發(fā)生1次β衰變．故B正確．
C、Th衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_DA/5.png">Pb，質(zhì)量數(shù)少24，知經(jīng)過6次α衰變，電荷數(shù)少8，知發(fā)生4次β衰變．故C正確．
D、U衰變?yōu)?img src="http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131028203419780197762/SYS201310282034197801977004_DA/7.png">Rn，質(zhì)量數(shù)少16，知經(jīng)過了4次α衰變，電荷數(shù)少6，知發(fā)生2次β衰變．故D錯(cuò)誤．
故選BC．
點(diǎn)評(píng)：解決本題的關(guān)鍵知道α衰變、β衰變的實(shí)質(zhì)，知道在衰變的過程中電荷數(shù)守恒、質(zhì)量數(shù)守恒．