2001 年

Radium (${}^{226}_{88}\mathrm{Ra}$) decays by emitting an $\alpha$ particle to form a product nucleus $X$. Which of the following shows the correct equation for this decay ?

The initial activity of a radioactive isotope is $2000$ Bq. After $4$ hours, the activity of the isotope drops to $125$ Bq. Find the half-life of the isotope.

The below shows part of a radioactive series. $P\xrightarrow{\alpha}Q\xrightarrow{\beta}R\xrightarrow{\beta}S$ Which of the following nuclei are isotopes of the same element ?