The formation of the volume electric charge in dielectrics containing radioactive β-isotope has been theoretically proposed. A method of calculating the value of the charge for both uniform and nonuniform distribution of the isotope in the volume is described. The method of the “acoustic sounding” has been used for the experimental study of charge distribution in the sample of crystalline Y3Al5O12(90Y) and borosilicate glass (90Sr +90Y). The results obtained are in good accord with the theoretical evaluations. A conclusion has been drawn to the effect that the measurement of volume charge distribution can be used to study the absorption of β-radiation in a substance and spatial distribution of β-isotope in the material.