This nucleus of radium-226, the one discovered by Marie Curie, decays directly in 93 % of the cases in a nucleus of radon by emitting an alpha particle. However in 7 % of the cases, the nucleus is left in an excited state. Very rapidly, the excited radon nucleus get rid of its excess of energy, by emitting a gamma ray. Physicists represents the various decays modes of a nucleus by decay charts similar to the one represented on the right. The emission of gamma very often accompany the transformations of nuclei.