A radioactive isomer has been found in ${\mathrm{Te}}^{121}$ with the help of a curved crystal x-ray spectrograph. The pair consists of a new 17±1-day activity produced by the reactions $\mathrm{Sb} \mathrm{}(d,2n)\mathrm{}$ and $\mathrm{Sb} \mathrm{}(p,n)\mathrm{}$ and a previously assigned activity evaluated here as 143±5 days. Sb and Te x-rays, a 0.61-Mev gamma-ray, a 0.223-Mev gamma-ray, and conversion electrons are associated with the long period. Sb x-rays and a 0.61-Mev gamma-ray are associated with the short period. The observations are simply explained by the isomeric transition. No evidence of the "fast" gamma-transition was found.

• Received 10 November 1945

DOI:https://doi.org/10.1103/PhysRev.69.140