Abstract <p>This paper discusses the use of Monte Carlo method to determine the γ-radiation dose rate and the flux of beta particles generated by radioisotope power sources based on such β emitters as ⁹⁰Sr/⁹⁰Y and ⁹⁹Tc. The features of modeling and the results of experiments aimed at checking the accuracy and reliability of the data obtained are described. Shielding efficiency of various materials for a specific layout of a power source assembly is calculated. The most effective shielding material is proposed in cases requiring dose rate minimization.</p>