|Cascade of gamma|
Gamma radioactivity generally accompanies alpha or beta decay, as this example of cobalt 60 shows. The nucleus of Cobalt-60 (a radioisotope with a half-life of 5,271 years) decays by undergoing beta radioactivity and forms a stable nucleus of nickel 60 The transformation, accompanied by the emission of an electron and an antineutrino, results in an excited nickel 60 nucleus 999 times out of 1,000. The nucleus loses the 2,158.80 keV of its excess energy by emitting a first gamma photon, followed by a second. The emission of the two photons follows hard on the heels of the electron and the antineutrino. The mass energy of the nickel 60 atom has been taken as zero in the scale shown above.