WAVE-VECTOR DEPENDENCE IN QUASI-ELASTIC NEUTRON-SCATTERING

The wave-vector (k) dependence of the quasielastic (QE) intensity gene rated by neutrons scattered by particles moving under the action of on e-dimensional potentials and weak stochastic forces is investigated in detail. It is shown that, in the low-k limit, the quasielastic intens ity due to scatterers subject to symmetric potentials is proportional to k(4), while asymmetric potentials will generally give rise to a k(2 ) term. Formulas to evaluate the coefficient for an arbitrary term in a k expansion of the cross section are derived. It is also shown that the QE line consists of a superposition of Lorentzians generated by en ergy relaxation modes. A possible application to the soft-potential mo del of glasses is indicated. [S0163-1829(97)03741-7].