LOW ENERGY NEUTRON CROSS SECTION OF MANGANESE

Abstract

The total neutron cross section of Mn55 has three (predominantly scattering) resonances in the energy range 300–2500 ev. In the present paper these resonances are examined in detail from the point of view of the R matrix formalism. It is found that quite good (but not perfect) agreement with the experimental cross section curve is obtained by assigning (in order of increasing resonance energy) spins (2, 3, 3) and neutron widths (23, 11, 395 ev.) to the resonances. The addition of a constant increment ΔR11 = 0.16 × 10−12 cm. representing the contribution of distant, positive energy, J = 3 resonances to the R matrix element for s-neutron scattering improves agreement with experiment on the high energy side of the highest energy resonance. The (n, γ) cross section at 0.025 ev. is fitted well by a constant radiation width of 0.5 ev. However, with no set of parameters was it possible to fit both the experimental total cross section curve, and the observed coherent scattering cross section at 0 ev., although the sign of the latter was accounted for correctly. The discrepancy is 2.0 barns (calculated) compared to 1.7 barns (observed).