CHEMICAL B INDING EFFECTS ON RESONANT SCATTERING OF NEUTRONS

Abstract Earlier calculations of the chemical binding effect on neutron resonance broadening do not agree with experimental results, A possible source of this difference is that the calculations have only examined the effect of chemical binding on resonant absorption and have not investigated the effect on resonant scattering. It is vital that we understand the discrepancy between the computed and measured chemical binding effect. Therefore the resonant differential scattering cross section is calculated for a harmonic rystal model to examine the chemical binding effect for resonant scattering, We show that. at high temperatures or high resonance nergies, scattering can be treated using ideal gas with the same effective temperature as for absorption accounting for chemical binding effects. Although the resonance broadening is determined in terms of a four-point correlation function, it is l\mnd that this broadening can still be written in terms of the usual 0-function and the effect of chemical binding in both resonance absorption and scattering is not large enough to account for the large measured effect. Thus the experiments that show a substantial mount of chemical binding must be reevaluated. The broadening ot " neutron scattering and absorption resonances by the thermal motions of the target atoms is referred to as "Doppler broadening". Doppler broadening is known to depend upon the state of the ato