The ratio of the real part to the imaginary part of the nucleon-nucleon elastic scattering amplitude is studied in terms of powers of the momentum transfer squared q². This study includes the dependence on the phase variation of the nucleon-nucleon elastic scattering amplitudes. The Gaussian form of the effective nucleon--nucleon interaction is used to calculate the nucleon--nucleon elastic scattering amplitudes. Analytical expressions for the phase variation and for the ratios of the real to the imaginary parts are obtained. The obtained expressions are new formulae and are found to be important for the description of nucleon-nucleon elastic scattering amplitudes. Introducing of the phase variation and the ratio of the real to the imaginary parts of the elastic scattering amplitude proportional to q² improves the theoretical calculations.

PACS numbers: 13.75.Cs, 21.30.-x, 24.10.-i, 25.55.Ci