${\mathrm{Er}}^{172}$ has been produced by double neutron capture in enriched ${\mathrm{Er}}^{170}$. The beta decay of 50.4-hr ${\mathrm{Er}}^{172}$ and its daughter, 63.7-hr ${\mathrm{Tm}}^{172}$, has been studied with a solenoidal beta spectrometer and beta and gamma scintillation spectrometers. The highest energy group of the ${\mathrm{Tm}}^{172}$ beta spectrum has an end-point energy of 1.83 Mev; this group represents the ${\mathrm{Tm}}^{172}$ → ${\mathrm{Yb}}^{172}$ ground-state beta transition. The beta decay of ${\mathrm{Tm}}^{172}$ is accompanied by gamma rays of the following energies: 0.079, 0.180, 0.422, 0.495, 0.915, 1.095, 1.29, 1.39, 1.41, 1.47, 1.51, and 1.59 Mev. A decay scheme for ${\mathrm{Tm}}^{172}$ is proposed with excited states in ${\mathrm{Yb}}^{172}$ at 0.079, 0.259, 1.174, 1.47, 1.55, 1.59, and 1.67 Mev. The beta decay of ${\mathrm{Er}}^{172}$ is accompanied by gamma rays of the following energies: 0.050 (Tm $K$ x ray), 0.108, 0.126, 0.408, and 0.610 Mev, the last of which represents a transition to the ${\mathrm{Tm}}^{172}$ ground state. The beta spectrum measured in coincidence with the 0.610-Mev gamma ray has an end-point energy of ∼0.26 Mev, which establishes a decay energy of 0.87 Mev for ${\mathrm{Er}}^{172}$.

• Received 6 January 1961

DOI:https://doi.org/10.1103/PhysRev.122.1295