Radioactive substances do not emit

Explain decay constant and write down its definition.

A sample contains $10^{-2}\, kg$ each of two substances A and $B$ with half lives $4 \,s$ and $8 \,s$ respectively. The ratio of then atomic weights is $1: 2$ The ratio of the amounts of $A$ and $B$ after $16 \,s$ is $\frac{x}{100}$. the value of $x$ is........

The disintegration rate of a certain radioactive sample at any instant is $4250$ disintegrations per minute.$10$ minutes later, the rate becomes $2250$ disintegrations per minute. The approximate decay cons $.........\min^{-1}$

Certain radioactive substance reduces to $25\%$ of its value in $16\ days$. Its half-life is .......... $days$

The decay constants of a radioactive substance for $\alpha $ and $\beta $ emission are ${\lambda _\alpha }$ and ${\lambda _\beta }$ respectively. If the substance emits $\alpha $ and $\beta $ simultaneously, then the average half life of the material will be