Gamma Rays Following Resonant Neutron Capture inFe56

Abstract

The spectrum of $\gamma$ rays following neutron capture at the 1167-eV resonance in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ has been measured at 90° and 135° to the incident beam. The partial widths for radiative decay have been determined and compared to the Weisskopf estimates. The $M1\mathrm{}$ and $E1\mathrm{}$ $\gamma$-ray strengths are found to be comparable, and a sizable $E2\mathrm{}$ $\gamma$ ray in the resonance has been recorded. On the basis of the $\gamma$-ray measurements at two angles, and from what has been determined from other experiments, the spin and parity of the 1167-eV resonance are shown to be ${\mathrm{½}}^{-}$.