Low-Lying States in ${\mathrm{Rb}}^{86}$ from ($d, p$), ($d, t$), and ($n, \gamma$) Reactions

The energy levels of ${\mathrm{Rb}}^{86}$ have been studied through the neutron stripping and pickup reactions ${\mathrm{Rb}}^{85}(d, p){\mathrm{Rb}}^{86}$ and ${\mathrm{Rb}}^{87}(d, t){\mathrm{Rb}}^{86}$, and the thermal-neutron-capture reaction ${\mathrm{Rb}}^{85}(n, \gamma ){\mathrm{Rb}}^{86}$. Enriched targets were bombarded with 12-MeV deuterons, and proton and triton spectra were observed with a magnetic spectrograph; proton angular distributions were compared with a distorted-wave Born-approximation (DWBA) calculation. Thermal-neutron-capture $\gamma$-ray spectra from both enriched ${\mathrm{Rb}}^{85}$ and natural rubidium targets have been studied in the energy intervals 50-2000 keV and 5000-8500 keV with a Ge(Li) spectrometer system. 32 low-energy $\gamma$-ray transitions were incorporated into a level scheme defined by the combined ($d, p$), ($d, t$), and the primary ($n, \gamma$) measurements. Tentative spin and parity assignments for 18 levels below 1505 keV are proposed on the basis of assigned orbital angular momentum transfers and $\gamma$-ray population and decay modes. The low-lying states of ${\mathrm{Rb}}^{86}$ are discussed in terms of shell-model proton-neutron configurations; comparison is made with a zero-range spin-dependent calculation. Although correlation between the data and positive parity levels predicted by the simple model is not entirely satisfactory, reasonable agreement has been found for low-lying negative parity levels.