The decay of ${}_{64}{}^{}{}_{}{}^{}\mathrm{Gd}_{}^{161}{}_{}{}^{}$(3.73 min) is characterized by beta emission to excited states in ${}_{65}{}^{}{}_{}{}^{}\mathrm{Tb}_{}^{161}{}_{}{}^{}$. This activity has been investigated by means of the Argonne 256-channel scintillation coincidence spectrometer and photographic internal-conversion-electron spectrographs. Sources were prepared by neutron irradiation of Gd, enriched in ${\mathrm{Gd}}^{160}$, in the Argonne reactor, CP-5. The presence of three beta-ray branches is deduced; two of these were observed experimentally by means of absorption methods. Fourteen gamma rays are reported. These radiations are fitted into a decay scheme which indicates excited states in ${\mathrm{Tb}}^{161}$ at 56.6, 134.0, 315.3, 417.6, 480.6, and 586.1 kev. A rotational band, based on the ground state and including the first two excited states, is indicated. Spin and parity assignments are also suggested for the third and fourth excited states.

• Received 23 December 1958

DOI:https://doi.org/10.1103/PhysRev.115.174