Electron Longitudinal Depolarization with Great Energy Loss

The average longitudinal depolarization of $\beta$ particles of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$+${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$, which have lost a great fraction (up to 70%) of their energy in aluminum, has been measured in the energy ranges 0.35-1.1, 0.35-2.2, and 0.9-2.2 MeV. The results are discussed with reference to different theoretical pictures of the depolarization process; the results agree, within the errors, with the depolarizations calculated on the basis of the theory given by Braicovich.