The $_{88}Ra^{226}$ is

Which metal is used in radiation shielding?

In radioactive decay,which one of the following moves the fastest?

The disintegration of an isotope of sodium,$_{11}Na^{24} \to _{12}Mg^{24} + _{-1}e^0$,shown is due to

The value of one microcurie $=$ $.......$ disintegrations / second

After losing a number of $\alpha$ and $\beta$ particles,$_{92}U^{238}$ changed to $_{82}Pb^{206}$. The total number of particles lost in this process is