Nickel-65 produced by a Ni/sup 64/(n, gamma y)Ni/sup 62/ reaction has a 2.56-hr half life and decays by emission of a beta particle to Cu/sup 65/. The decay takes place by 57% 2.10-Mev beta, 29% 0.60-Mev beta, and 14% 1.0-Mev beta. These are accompanied by emission of gamma rays having energies of 1.49 Mev, 1.12 Mev, and 0.37 Mev. Nickel65 activity can be measured by counting the beta particles, the gross gamma energies, or discrete gamma energies. (W.L.H.)