Orientation-Averaged Amplitude of the One-Quantum Term in the Neutron Scattering Law for Molecular Gases

The amplitude of the one-quantum term in the scattering law for coherent scattering of neutrons by molecular gases is calculated using a generating-function approach. The phase factor exp (iκ·b) is averaged jointly with the amplitude factor (κ·γν) (κ·γν′), as opposed to the more common technique of approximating the joint average by the product of the average of each factor. Results of example calculations show that the correction is of the same magnitude as the result of the conventional calculation.