Radioactive substances emit $\gamma$-rays,which are

The radiations having high penetrating power and not affected by electrical and magnetic field are

Who developed the study of radioactivity?

If uranium (mass number $238$ and atomic number $92$) emits an $\alpha$-particle,what are the mass number and atomic number of the product?

$\beta$-emission is always accompanied 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