Half life of radium is $1620$ years. How many radium nuclei decay in $5$ hours in $5\, gm$ radium? ( Atomic weight of radium $= 223$)
$9.1 \times 10^{12}$
$3.23 \times 10^{15}$
$1.72 \times 10^{20}$
$3.3 \times 10^{17}$
The half life of a radioactive substance is $20$ minutes. The approximate time interval $(t_2 -t_1)$ between the time $t_2$ when $3/4$ of it has decayed and time $t_1$ when $1/4$ of it had decayed is
Why radioactivity is considered a nuclear phenomenon ?
A radioactive element has half life period $800$ years. After $6400$ years what amount will remain?
The activity of a radioactive sample falls from $700 \;\mathrm{s}^{-1}$ to $500\; \mathrm{s}^{-1}$ in $30\;min$. Its half life is close to.........$min$
Half life of $B{i^{210}}$ is $5$ days. If we start with $50,000$ atoms of this isotope, the number of atoms left over after $10$ days is