Alpha particles are made up of two protons and two neutrons and are emitted by certain types of radioactive material. They have a positive charge and are relatively large and heavy, so they are easily stopped by matter and do not penetrate very far. Alpha particles are typically stopped by a sheet of paper or a few centimeters of air and are not able to penetrate most materials.

Gamma rays, on the other hand, are electromagnetic radiation with extremely short wavelengths and high energy. They are produced by nuclear reactions and are often emitted along with alpha particles and other types of radiation. Gamma rays are able to penetrate matter more deeply than alpha particles and can pass through thick layers of metal, concrete, and other materials. They are more difficult to shield against and can pose a serious health hazard if not properly protected against.