First 3- excited state of 56Fe

There is no reliable evidence for the existence of the 3.076 MeV (3(-)) level adopted in the ENSDF evaluation for Fe-56 although it has been reported in a few experiments. Previous reports of the observation of this level appear to be based on an incorrect assignment in early (e, e') work. Recent neutron inelastic scattering measurements by Demidov et al. [Phys. At. Nucl. 67, 1884, (2004)] show that the assigned gamma-ray decay of this state does not occur at a level consistent with known properties of inelastic scattering. In the present work the Fe-56( n, n'gamma) reaction was used to populate excited states in Fe-56. Neutrons in the energy range from 1 to 250 MeV were provided by the pulsed neutron source of the Los Alamos Neutron Science Center's WNR facility. Deexciting gamma rays were detected with the GEANIE spectrometer, a Compton suppressed array of 26 Ge detectors. The gamma-gamma data obtained with GEANIE were used to establish coincidence relations between transitions. All previously reported levels up to E-x = 3.6 MeV excitation energy were observed except for the 3.076 MeV (3(-)) level. The 991- and 2229-keV transitions, previously reported to deexcite this level, were not observed in the gamma-gamma coincidence data obtained in the present experiment. The present work supports the assignment of the 4509.6 keV level as the first 3(-) excited state in Fe-56 by observation of two previously known transitions deexciting this state.