Question

²³⁸U的半衰期是4.5×10⁹年，假設(shè)一塊礦石中含有2 kg的²³⁸U.求：

(1)經(jīng)過45億年后，還剩多少²³⁸U?

(2)假設(shè)發(fā)生衰變的鈾都變成了²⁰⁶Pb，礦石中含有多少鉛？

(3)這時鈾、鉛的質(zhì)量之比是多少？

Answer 1

(1)1 kg  (2)0.866 kg  (3)1∶0.866

解析:

(1)45億年是²³⁸U的半衰期，這樣還剩²³⁸U為1 kg.                                   (3分)

(2)1 kg的²³⁸U衰變?yōu)?sup>206Pb，則鉛的質(zhì)量為

×1 kg=0.866 kg.                                                                                      (3分)

(3)鈾、鉛的質(zhì)量之比為1∶0.866                                                                     (2分)