2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/82687A nonstandard method for calculating the nuclear $2νββ$ - decay amplitude is proposed. The method is based on the explicit use of those approximate symmetries of a nuclear hamiltonian, which correspond to the operators of allowed $β$ -- transitions. Within the framework of the proposed method the mentioned amplitude is calculated for a wide range of nuclei. The model parameters used in calculations are taken from independent data. Calculated \bb half-lifes are compared with known experimental data.LaTeX, 10 pagesNuclear Theorytext