Question

$1g$ radium is reduced by $2.1mg$ in $5$ years by alpha decay, calculate the half-life period.

Answer 1

Mass of radium left after $5$ years $=(1.0-0.0021)g$ $=0.9979g$
Apply, $\lambda =\frac{2.303}{t}{\log }_{10}\frac{N_0}{N}=\frac{2.303}{5}{\log }_{10}\frac{1}{0.9979}$