Decay ofTm172

The radioactive nuclide ${}_{69}{}^{}{}_{}{}^{}\mathrm{Tm}_{}^{172}{}_{}{}^{}$ was produced by successive capture of two neutrons in erbium oxide enriched in ${\mathrm{Er}}^{170}$. The irradiations were made in the Materials Testing Reactor at Arco, Idaho. In addition to three thulium activities, these samples contained six active contaminants. Pure thulium sources were obtained by use of an ion-exchange column. Studies were conducted with a 256-channel coincidence scintillation spectrometer. These measurements indicate the presence of at least 17 gammaray and 5 beta-ray transitions. The beta-ray spectrum was studied with a 180° magnetic beta-ray spectrometer. This spectrum was analyzed by use of a computer program compiled by the authors in collaboration with members of the Argonne Applied Mathematics Division. The level scheme proposed for ${\mathrm{Yb}}^{172}$ has states with energies, spins, and parities of 0.0($0^{+}$), 0.079($2^{+}$), 0.260($4^{+}$), 1.17(3), 1.46(2), 1.54(3), 1.60(1), 1.64(?), and 1.73(3) Mev. The total decay energy is found to be 1.88 Mev. The experimental data are consistent with the previously proposed interpretation that the first two excited states are members of a $K=0\mathrm{}$ rotational band based on the ground state. The states at 1.46 and 1.54 Mev are interpreted as members of a rotational band with $K=2\mathrm{}$. The states at 1.60 and 1.73 Mev are tentatively interpreted as members of a rotational band with $K=0\mathrm{}$ and negative parity. It is suggested that the state at 1.17 Mev has $K=3\mathrm{}$. From the analysis of the beta spectrum it is concluded that the ground state of thulium has $I=K=2\mathrm{}$ and negative parity.