Absolute measurement of the critical scattering cross section in cobalt

Small‐angle neutron scattering techniques have been used to study the angular distribution of the critical scattering from cobalt above Tc. These measurements have been put on an absolute scale by calibrating the critical scattering directly against the nuclear incoherent scattering from cobalt. In this way the interaction range r1, which appears in the classical and modified Ornstein‐Zernike expressions for the asymptotic form of the spin pair correlation function and is related to the strength of the spin correlations, has been determined. We obtain r1/a=0.46±0.03 for the ratio of the interaction range to the nearest‐neighbor distance in cobalt. This result is in good agreement with theoretical predictions. Lack of agreement among previous determinations of the ratio r1/a made in iron failed to provide a definitive comparison with theory.