Gamma decay happens when a nucleus produces a high-energy packet of energy called a gamma ray. Gamma rays do not have electrical charge, but they do have angular momentum. Gamma rays are usually emitted from nuclei just after other types of decay. Gamma rays can be used to see through material, to kill bacteria in food, to find some types of disease, and to treat some kinds of cancer. Gamma rays have the highest energy of any electromagnetic wave, and gamma ray bursts from space are the most energetic releases of energy known.