Which of the following can pass through $20 \, cm$ thickness of steel?

When $_{90}Th^{238}$ transforms into $_{83}Bi^{222}$,the number of $\alpha$ and $\beta$ particles emitted are:

$A$ sample of a radioactive nucleus $A$ disintegrates to another radioactive nucleus $B$,which in turn disintegrates to some other stable nucleus $C$. Plot a graph showing the variation of the number of atoms of nucleus $B$ versus time:
(Assume that at $t=0$,there are no $B$ atoms in the sample)

In the uranium radioactive series,the initial nucleus is ${ }_{92}^{238} U$ and the final nucleus is ${ }_{82}^{206} Pb$. When the uranium nucleus decays into lead,the number of $\alpha$-particles and $\beta$-particles emitted are

When a nucleus with atomic number $Z$ and mass number $A$ undergoes a radioactive decay process:

Which of the following physical quantities is measured using the unit $rad$?