[en] The problem of scattering of long-wave neutrons on the ion crystal lattice defects is solved in the harmonic approximation. The numerical calculations of the differential cross section of the neutron scattering on Cl vacancies in NaCl for the wavelength of 5.5; 7 and 9A are carried out for the case when the initial neutron momentum with the Λ wavelength is directed along the crystal axis (100). The whole region of static nonordering are taken into account in calculations. It is shown that except the region of small scattering angles, the behaviour of the cross section qualitatively coincides with the results of other authors and has a smooth character