Gamma-Ray Spectrum from Thermal-Neutron Capture inSm149, and Associated Energy Levels inSm150

The gamma-ray spectrum resulting from thermal-neutron capture in ${\mathrm{Sm}}^{149}$ was investigated with the Argonne 7.7-m bent-crystal spectrometer. The observed spectrum consisted of 217 gamma rays with energies between 40 keV and 2.4 MeV. The bent-crystal gamma-ray data were combined with the conversion-electron data of Bieber et al. and Groshev et al. to obtain $K$ conversion coefficients for fifty of the observed gamma-ray transitions. These precision measurements of gamma-ray energies, intensities, and conversion coefficients were combined with a set of $\gamma -\gamma$ coincidence and $\gamma -\gamma$ angular-correlation measurements [with a similar source of ${\mathrm{Sm}}^{149}(n,\gamma ){\mathrm{Sm}}^{150}$ gamma rays] to develop a partial level scheme for ${\mathrm{Sm}}^{150}$, in which the excitation energies (keV) and the spins and parities (in brackets) are: ground state [$0^{+}$], 333.94[$2^{+}$], 740.43[$0^{+}$], 773.33[$4^{+}$], 1046.13[$2^{+}$], 1071.39[$3^{-}$], 1165.57[$2^{+}$], 1193.83[$2^{+}$], 1278.78[$3^{+}$], 1357.55[$3^{-}$], 1449.11[$4^{+}$], 1504.48[$3^{+}$], and 1642.55[$4^{+}$]. In this partial level scheme, the spin and parity assignments for all 14 levels are uniquely defined. The energy levels at 1279.05, 1449.15, and 1504.42 keV are of particular interest because they exhibit strong $E2\mathrm{}$ transitions to the $4^{+}$ state at 773.51 keV and suggest the presence of strong collective components in their wave functions. The previously published radioactivedecay, ($n,\gamma$), and charged-particle work on ${\mathrm{Sm}}^{150}$ were then combined with the crystal diffraction data to define twelve additional levels in ${\mathrm{Sm}}^{150}$. This extended level scheme of ${\mathrm{Sm}}^{150}$ agrees well with much of the previously published work and removes many of the previous uncertainties in the level scheme.