Energy levels of Nickel 60:
This diagram represents the energy ladder of a nickel 60 nucleus (product of the decay of the cobalt-60), whose rungs indicate the energy levels the nucleus can reach. The lowest called the ground state, represents the energy of a nucleus at rest. If raised to any of the higher levels, the nucleus immediately emits one or more characteristic gamma rays, lowering its energy sufficiently to allow it to regain the ground state. These energies are calculated by taking the difference between the (very accurately measured) departure and arrival energies. The transitions numbered 4 and 5, by far the more common, have been represented with thicker arrows.