Low-lying dipole excitations in the odd-proton, midshell nucleus ${}^{103}\mathrm{Rh}$

Low-lying dipole excitations in the odd-proton, midshell nucleus ${}^{103}\mathrm{Rh}$ were investigated in photon scattering experiments at the Stuttgart Dynamitron facility using bremsstrahlung beams with end point energies of 4.1 and 2.4 MeV. In total, 106 excited levels, most of them unknown so far, could be observed in the excitation energy range from 1.2 to 4.0 MeV. In addition to 106 transitions to the ground state ${(J}_0^{\pi }{=1/2\mathrm{}}^{-}),$ 20 transitions to the low-lying $J^{\pi }{=3/2\mathrm{}}^{-}$ level at 295 keV and 10 transitions to the $J^{\pi }{=5/2\mathrm{}}^{-}$ state at 357 keV were detected. For 20 photoexcited levels spins could be suggested from the measured angular distribution data. The reduced ground-state transition strengths summed up in the energy range 2–4 MeV amount to $\Sigma g{\Gamma }_0^{\mathrm{red}}=(16.3\mathrm{}\pm 1.9)$ ${\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{M}\mathrm{e}\mathrm{V}}^3$ corresponding, under the assumption of an electric character for all excitations, to a total excitation strength of $\Sigma B\left(E1\mathrm{}\right)\mathrm{}\uparrow =(15.6\mathrm{}\pm 1.8)\times {10}^{-3}$ $e^2{\mathrm{fm}}^2.$ The fragmentation of the dipole strength and the decay branchings of the photoexcited levels are discussed. The observed feedings of the 295 and 357 keV levels result in a population inversion, the precondition for a possible $\gamma$-ray laser.