Search for direct neutron capture in manganese

Abstract

A search for the existence of the direct neutron capture reaction mechanism in the radiative capture of low-energy neutrons in manganese is reported. Using the Yale electron Linac to produce pulsed neutrons, the neutron energies were selected by the time-of-flight technique while the γ-rays were detected in a NaI(Tl) anticoincidence spectrometer. The shape of the partial capture cross section for emission of the 7.26 MeV ground state γ-ray was measured as a function of neutron energy. The amount of direct capture was to be identified by the expected interference between direct and resonance capture near the 337 eV resonance. At 1 eV neutron energy an upper limit of 160 mb was established for the direct capture cross section. If it is assumed that the partial radiation widths and phase factors for the bound level at −2830 eV and for the 337 eV resonance are the same then the upper limit of ≈ 30 mb is obtained. The accuracy of these results was limited by the multiple scattering in the sample and by the uncertainty in the bound level parameters. However, the experimental results cannot be accounted for without interference effects in the capture mechanism.