The ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}(n, \gamma ){}_{}{}^{153}{}_{}{}^{}\mathrm{Sm}$ spectrum was measured with the Argonne bent-crystal spectrometer and with a Ge(Li) detector at the in-pile facility at the Argonne CP-5 research reactor. The low-energy bent-crystal spectrum consisted of 251 $\gamma$ transitions associated with thermal-neutron capture in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}$, with energies between 28 and 1041 keV. The $\gamma$-ray intensities were normalized to the previously established intensity of the 103-keV line in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Eu}$ from the $\beta$ decay of ${}_{}{}^{153}{}_{}{}^{}\mathrm{Sm}$. The energies and intensities of 24 other lines associated with this $\beta$ decay are also given. The high-energy ($n, \gamma$) spectrum, containing 23 lines between 4.5 and 5.9 MeV, was obtained with a Ge(Li) detector. The neutron binding energy of ${}_{}{}^{153}{}_{}{}^{}\mathrm{Sm}$ was found to be 5869.3±2.0 keV. The conversion-electron spectrum, measured with the high-resolution magnetic spectrometer at Munich, was used to obtain $K$ and $L$ conversion coefficients and corresponding multipole assignments for 37 of the low-energy $\gamma$ transitions. The $\gamma$ spectrum in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Sm}$ following $\beta$ decay of ${}_{}{}^{153}{}_{}{}^{}\mathrm{Pm}$ was measured with Ge(Li) and Si(Li) detectors. The source was made at Darmstadt through the ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}(\gamma , p){}_{}{}^{153}{}_{}{}^{}\mathrm{Pm}$ reaction. The ($n, \gamma$), ($n, e^{-}$), and $\beta$-decay experiments were combined to develop the level scheme of ${}_{}{}^{153}{}_{}{}^{}\mathrm{Sm}$, in which unique spin and parity assignments are made for 13 of the 28 levels below 750 keV. The energy (keV) and $J^{\pi }$ of the first 28 levels are: 0.000, ${\frac{3}{2}}^{+}$; 7.535, ${\frac{5}{2}}^{+}$; 35.843, ${\frac{3}{2}}^{-}$; 53.533, ${\frac{7}{2}}^{+}$ or (${\frac{5}{2}}^{+}$); 65.475, ${\frac{9}{2}}^{+}$ or ${\frac{7}{2}}^{+}$ or ${\frac{5}{2}}^{+}$; 90.874, ${\frac{5}{2}}^{-}$; 112.954, ${\frac{9}{2}}^{+}$ or ${\frac{7}{2}}^{\pm }$ or ${\frac{5}{2}}^{\pm }$; 127.298, ${\frac{3}{2}}^{-}$; 174.17, ${\frac{7}{2}}^{-}$; 182.90, ${\frac{5}{2}}^{-}$; (194.65), ${\frac{5}{2}}^{\pm }$ or ${\frac{7}{2}}^{+}$; 262.33, ${\frac{7}{2}}^{+}$ or (${\frac{5}{2}}^{+}$); (265.93), ${\frac{7}{2}}^{-}$ or (${\frac{5}{2}}^{\pm }$); 276.71, ${\frac{3}{2}}^{+}$; 321.11, ${\frac{3}{2}}^{+}$; 356.69, ${\frac{5}{2}}^{+}$; 362.29, ${\frac{5}{2}}^{+}$; (371.04), $\frac{9}{2}$ or $\frac{7}{2}$; 405.46, ${\frac{3}{2}}^{-}$; 414.91, ${\mathrm{½}}^{+}$ or ${\frac{3}{2}}^{+}$; 447.07, $\frac{5}{2}$ or $\frac{7}{2}$; 450.04, $\frac{5}{2}$ or $\frac{7}{2}$; 481.08, ${\frac{3}{2}}^{+}$; 524.36, $\frac{5}{2}$; 630.20, ${\frac{3}{2}}^{\mathrm{}(-)\mathrm{}}$; 695.83, ${\mathrm{½}}^{\mathrm{}(+)\mathrm{}}$ or ${\frac{3}{2}}^{\mathrm{}(+)\mathrm{}}$; 734.90, $\frac{5}{2}$; and 750.32, ½ or $\frac{3}{2}$. The parentheses around a level energy or spin assignment mean that this value is less well established or is less probable if there is a choice. Of special interest is the very low-energy (7.53 keV) first excited state with $J^{\pi }={\frac{5}{2}}^{+}$, which appears to be the second member of the strongly distorted ground-state rotational band. A good match between the theoretical predictions of the Nilsson model and the observed $\gamma$-ray branching ratio was obtained when nine of the eleven levels below 200 keV were assigned to a positive-parity, $K=\frac{3}{2}$, ground-state rotational band and two negative-parity, $K=\frac{3}{2}$, rotational bands with band heads at 35.84 and 127.30 keV.

• Received 29 May 1969

DOI:https://doi.org/10.1103/PhysRev.187.1632