The observation of critical narrowing in molten 7Li0.62Na0.38 by quasi-elastic neutron scattering

We report the first direct observation of critical narrowing by quasi-elastic neutron scattering. A molten 7Li0.62Na0.38 alloy has been studied close to the critical point of phase separation (Tc = 576 K) using the IRIS spectrometer at ISIS (Rutherford Appleton Laboratory) with mica (002) analysers (energy resolution 1 μeV) and the lowest available scattering angles (Q ∼ 0.15 A-1). The fitted quasi-elastic line widths are found to be intermediate between the values for normal diffusion and the behaviour predicted inside the critical region. For the (Q, ω) range covered this is in accord with expectations based on previously determined critical coefficients. The experimental requirements for a detailed study of the critical dynamics are discussed. (orig.)