α sources emit alpha particle beams. The energy of alpha particle is about 5 Mev, with 4 cm range in the air and 10~20 µm range in the solid. Particular attention should be given to the integrity of window due to the high toxicity of alpha sources, and care must be taken to prevent the ingestion of radioactive elements. ²³⁸Pu α source is prepared by powder metallurgy technique, with Au-Pd alloy cover and silver backing.