Angular Correlation of Gamma Cascades inGd155, and Levels ofGd155Populated by the Decay ofTb155

The level scheme of ${\mathrm{Gd}}^{155}$ has been studied using high-resolution Ge(Li), Si(Li), and standard scintillation counters. The analysis of the experimental data for this nucleus is impeded by an ambiguity in the spin values of the majority of its excitated states. In the present work $\gamma -\gamma$ angular correlations in the decay of ${\mathrm{Tb}}^{155}$-${\mathrm{Gd}}^{155}$ were measured using a Ge(Li) detector in coincidence with NaI(T1) scintillation counter. The spins of some of the levels up to the 648.1-keV level have been confirmed from various cascades. The analysis of the various coincidence experiments leads to the proposal of levels in ${\mathrm{Gd}}^{155}$ at 60.0, 85.5, 105.3, 118.0, 146.0, 235, 266.6, 268.6, 286.8, 326.0, 367.7, 427.4, 451.3, 488.8, 559.9, 592.6, 615.5, and 648.1 keV. A consistent level scheme of ${\mathrm{Gd}}^{155}$ is proposed and the spin and parity assignments of the levels are discussed. The multipolarity of the different $\gamma$ rays including the percentage of mixing is reported.