An accident in a nuclear laboratory resulted in deposition of a certain amount of radioactive material of half-life $18$ days inside the laboratory. Tests revealed that the radiation was $64$ times more than the permissible level required for safe operation of the laboratory. What is the minimum number of days after which the laboratory can be considered safe for use?

The activity of a radioactive sample is $1.6\, curie$ and its half-life is $2.5 \,days$. Its activity after $10\, days$ will be .......... $curie$

A mixture consists of two radioactive material $A_1$ and $A_2$ with half lives of $20\,s$ and $10\,s$ respectively . Initially the mixture has $40\,g$ of $A_1$ and $160\,g$ of $A_2$ . The amount of the two in the mixture will become equal after..........$sec$

Half life of a radio-active substance is $20\, minutes$. The time between $20\%$ and $80\%$ decay will be ........... $minutes$

The half-life of a radioactive substance is $T$. The time taken, for disintegrating $\frac{7}{8}$ th part of its original mass will be

A radioactive nucleus decays by two different processes. The half life for the first process is $10\, s$ and that for the second is $100 s$. the effective half life of the nucleus is close to$.....sec$