Thermal Neutron Capture Gamma Rays in Iron

The gamma rays of ${\mathrm{Fe}}^{57}$ emitted following thermal neutron capture in ${\mathrm{Fe}}^{56}$ have been investigated by the measurement of coincidences between a three-crystal pair spectrometer and a single NaI(Tl) crystal. These data have been combined with information about the levels of ${\mathrm{Fe}}^{57}$ derived from the decay of ${\mathrm{Co}}^{57}$, which has been re-examined here, the decay of ${\mathrm{Mn}}^{57}$, and nuclear reaction data in order to determine the properties of several of the low-lying levels in ${\mathrm{Fe}}^{57}$. The spins, parities, and decay characteristics of the first four excited states in ${\mathrm{Fe}}^{57}$ now appear to be established as well as the main features of the decay of the levels at 1.266, 1.630, and 1.728 Mev.