We have determined the half-life of ${}_{}{}^{131}{}_{}{}^{}\mathrm{I}$ samples to be 7.969±0.014 day under conditions in which the radiations of 12.0-day ${}_{}{}^{131m}{}_{}{}^{}\mathrm{Xe}$ are not detected, and to be 8.117±0.012 day under conditions in which the radiations of ${}_{}{}^{131m}{}_{}{}^{}\mathrm{Xe}$ are detected. Furthermore, we have seen no variations of half-life due to the physical state of the source to within 0.3%. We believe that these data indicate the half-life variations for ${}_{}{}^{131}{}_{}{}^{}\mathrm{I}$ reported by Bergamini et al. and Kemeny may be accounted for by the escape of daughter ${}_{}{}^{131m}{}_{}{}^{}\mathrm{Xe}$ and/or absorbtion of the radiations of ${}_{}{}^{131m}{}_{}{}^{}\mathrm{Xe}$.

• Received 14 December 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1699