Radon $({R_n})$ decays into Polonium (${P_0}$) by emitting an $\alpha – $ particle with half-life of $4\, days$. A sample contains $6.4 \times {10^{10}}$ atoms of $R_n$. After $12\, days$, the number of atoms of ${R_n}$ left in the sample will be

Half-life of a radioactive substance is $20\,minute$ . The time between $20\%$ and $80\%$ decay will be ……… $min$

A radioactive material decays by simultaneous emission of two particles with respective half lives $1620$ and $810$ years. The time (in years) after which one- fourth of the material remains is

A freshly prepared sample of a radioisotope of half-life $1386 \ s$ has activity $10^3$ disintegrations per second. Given that In $2=0.693$, the fraction of the initial number of nuclei (expressed in nearest integer percentage) that will decay in the first $80 \ s$ after preparation of the sample is :

For a radioactive material, half-life is $10$ minutes. If initially there are $600$ number of nuclei, the time taken (in minutes) for the disintegration of $450$ nuclei is