7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may be distinguished in terms of penetrating power

alpha particles are two neutrons and two protons; also known as a helium nucleus. Alpha particles could not penetrate a piece of paper if they tried.

Beta particles are electrons, they are emitted when a neutron turns into a proton and an electron. It won't penetrate aluminium.

Gamma rays are a type of electromagnetic wave, they are often emitted alongside the other types of radiation. Gamma cannot penetrate lead.