Near-harmonic structure and level similarities in Fe56, Fe58 and Ni60

Near-harmonic structure is known to exist in Fe58, and an investigation was undertaken to determine whether this structure is also present in Fe56, and Ni60. In the case of Fe56, no second 2+ state with the desired energy or de-excitation characteristics had been reported by previous investigators and a search for a small excitation of such a level from the decay of Mn56 is described. The results are inconclusive although some evidence for its existence is presented. Our investigation of the Mn56-Fe56 decay reveals the presence of an additional beta branch to a 2+ level at 3.34 Mev in Fe56. The results of the angular correlation measurements on the cascade gamma rays from this and other levels are given. The stopover transitions are found to be mostlyM 1 radiation and hence not of the near-harmonic type. In the case of Ni60, the measured angular correlation functions for the 0.85–1.33 and 1.76–1.33 Mev cascades initiated from the decay of Cu60 are reported. For the former cascade, the results indicate that the stopover transition is largely E2 radiation, but the experimental difficulties prevent a more quantitative statement. The presence of this type of radiation, together with a stopover to crossover intensity ratio of 15, imply the existence of near-harmonic structure in Ni60. The angular correlation function for the latter cascade is found to be nearly identical to that of the corresponding cascade in Fe58 which lends weight to the contention that there exist level similarities in these nuclei. Additional evidence for these similarities is also presented.