A heavy nucleus $Q$ of half-life $20$ minutes undergoes alpha-decay with probability of $60 \%$ and beta-decay with probability of $40 \%$. Initially, the number of Q nuclei is $1000$ . The number of alphadecays of $Q$ in the first one hour is
$50$
$75$
$350$
$525$
The half life of a radioactive substance against $\alpha - $ decay is $1.2 \times 10^7\, s$. What is the decay rate for $4.0 \times 10^{15}$ atoms of the substance
A radioactive substance has an average life of $5$ hours. In a time of $5$ hours
If ${N_0}$ is the original mass of the substance of half life period ${T_{1/2}} = 5$ years, then the amount of substance left after $15$ years is
The radioactivity of a given sample of whisky due to tritium (half life $12.3$ years) was found to be only $3\%$ of that measured in a recently purchased bottle marked $"7$ years old". The sample must have been prepared about
An archaeologist analyses the wood in a prehistoric structure and finds that ${C^{14}}$ (Half life $= 5700\, years$) to ${C^{12}} $ is only one- fourth of that found in the cells buried plants. The age of the wood is about ........$years$