Which metal is used in radiation shielding?

Which of the following isotopes of uranium is the most radioactive?

$\beta$-particle is emitted in radioactivity by

If by mistake some radioactive substance gets inside the human body,then from the point of view of radiation damage,the most harmful will be the one which emits

Radioactivity was discovered by

The number of $\alpha-$ and $\beta-$ particles emitted when a radioactive element $_{90}E^{232}$ changes into $_{86}G^{220}$ will be