The new isotopes ${\mathrm{Cs}}^{127}$ and ${\mathrm{Cs}}^{129}$ have been produced from iodine by irradiation with high energy helium ions. Their mass assignments were determined with a mass spectrograph. ${\mathrm{Cs}}^{127}$ decays with 5.5±0.5 hr. half-life with emission of positrons (1.2 Mev maximum energy), giving rise to the daughter activity 34-day ${\mathrm{Xe}}^{127}$. ${\mathrm{Cs}}^{129}$ decays by electron capture with half-life 31±1 hr. A 30-min. activity, presumed to be ${\mathrm{Cs}}^{130}$, was also produced, but its mass assignment is uncertain.

• Received 31 October 1949

DOI:https://doi.org/10.1103/PhysRev.77.614