[en] The absolute standardization of radioactive solutions of low energy beta emitters and beta-gamma emitters with a high probability of disintegration to the ground state is described; the tracer and the efficiency extrapolation methods were used. Both types of radionuclides were mathematically and physically treated in an unified manner. The theoretical relations between different beta spectra were calculated according to Williams' model and experimentally verified for: ³⁵S + ⁶⁰Co, ³⁵S + ⁹⁵Nb, ¹⁴⁷Pm + ⁶⁰Co, ¹⁴C + ⁹⁵Nb and two beta branches of ⁹⁹Mo. The optimum range of beta efficiency variation was indicated. The basic supposition that all beta efficieny tend to unity in the same time was experimentally verified, using two ¹⁹²Ir beta branches. Four computer programs, written in the FORTRAN IV language, were elaborated, for the adequate processing of the experimental data. Good precision coefficients according to international standards were obtained in the absolute standardization of ³⁵S, ¹⁴⁷Pm, ⁹⁹Mo solutions. (author)