Answer:
A piece of paper
Explanation:
The emitted radiations are helium nuclei which is also called alpha particle. The alpha radiations can be stopped by a piece of paper. While beta radiations can be blocked by the sheet of aluminium and Lead is used for the protection against gamma radiations because of its high molecular density.
Alpha radiations:
Alpha radiations are emitted as a result of radioactive decay. The atom emit the alpha particles consist of two proton and two neutrons. Which is also called helium nuclei. When atom undergoes the alpha emission the original atom convert into the atom having mass number 4 less than and atomic number 2 less than the starting atom.
Alpha radiations can travel in a short distance.
These radiations can not penetrate into the skin or clothes.
These radiations can be harmful for the human if these are inhaled.
These radiations can be stopped by a piece of paper.
