Precise measurement (approximately 1.6% relative error) of the spontaneous-fission decay constant of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ has been carried out with solid-state track recorders of pre-etched mica. The present experimental result, ${\lambda }_F=(7.03\mathrm{}\pm 0.11)\times {10}^{-17\mathrm{}}$ ${\mathrm{yr}}^{-1\mathrm{}}$, is within the quoted experimental error of earlier measurements both by Fleischer and Price, and by Rao and Kuroda. It is in good agreement with the value inferred by Fleischer and Price from a comparison of different dating methods.

• Received 22 January 1968

DOI:https://doi.org/10.1103/PhysRev.174.1482