Thermal and Resonance Neutron Capture in Copper, Nickel, and Manganese

The high-energy $\gamma$ rays following low-energy ($E_n<10\mathrm{}$ keV) neutron capture in copper, nickel, and manganese have been observed with a NaI(Tl) anticoincidence spectrometer. Large fluctuations in the intensities of ground-state transitions of the two copper isotopes were observed. The relative intensities of the high-energy transitions in both nickel and copper decrease significantly with neutron energy at only ∼1 keV. The variations of the twelve highest energy transitions for the three lowest energy resonances in manganese were measured. The 7.04-MeV transition varied by a factor of 25, while the rest showed much less fluctuation. None of the twelve transitions is appreciably correlated with the reduced neutron width.