A sample of a radioactive isotope has an initial activity of . Exactly later, its activity drops to — Nuclear Chemistry and Radioactivity Chemistry Question

Question

A sample of a radioactive isotope has an initial activity of $28\text{ dpm}$. Exactly $30\text{ minutes}$ later, its activity drops to $14\text{ dpm}$. What is the decay constant ($\lambda$) of this isotope? (Use $\ln 2 \approx 0.693$).