Gamma Rays from Thermal and Resonance Neutron Capture inSb121andSb123

Prompt high-energy $\gamma$ rays resulting from neutron capture at thermal energies and in the resonances of ${\mathrm{Sb}}^{121}$ and ${\mathrm{Sb}}^{123}$ have been studied with the high flux beam reactor fast chopper using high-resolution Ge(Li) detectors. The binding energy $B_n$ of the last neutron in ${\mathrm{Sb}}^{122}$ and ${\mathrm{Sb}}^{124}$ has been determined to be 6807 ± 2 and 6468 ± 2 keV, respectively. Based on prompt capture $\gamma$-ray data, we have assigned a spin of 4 to the 21.6-eV resonance of ${\mathrm{Sb}}^{123}$. Energy levels populated by the neutron-capture $\gamma$ rays are given up to an excitation energy of 2475 keV in ${\mathrm{Sb}}^{122}$ and up to 2221 keV in ${\mathrm{Sb}}^{124}$. These data are compared with the existing ($d,p$) data on ${\mathrm{Sb}}^{121}$ and ${\mathrm{Sb}}^{123}$. We have also studied the low-energy ($\gamma$ rays originating in neutron capture in the different resonances. For ${\mathrm{Sb}}^{121}$, the observed spectra are found to fall into two classes, each having its own characteristic intensity distribution depending on the spin of the capturing state. By comparing these spectra with those originating from the 6.24-eV resonance ($3^{+}$) and the 15.4-eV resonance ($2^{+}$), we have assigned the following spins to the resonances in ${\mathrm{Sb}}^{121}$: 29.7 eV (3), 53.5 eV (2), 64.5 eV (3), 73.8 eV (2), 111.4 eV (2), and 126.8 eV (3). Similar, but more tentative, spin assignments are made for resonances in ${\mathrm{Sb}}^{123}$.