Decay of 5.9-DayEu145to Levels inSm145

The level structure of ${}_{}{}^{145}{}_{}{}^{}\mathrm{Sm}$ was studied by observing the electron-capture decay of 5.9-day ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$. The radioactive source was prepared by bombarding ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ with protons accelerated in the Oak Ridge isochronous cyclotron. Both singles and $\gamma -\gamma$ coincidence spectra were measured. From these measurements, transition energies were obtained to an accuracy better than previously available and the following new transitions were assigned to the decay of ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$: 519.4, 526.2, 713.9, 910.3, 949.9, ∼1625, 2340.8, 2508.1, and 2513.0 keV. Because of decay-energy considerations the latter three transitions establish the existence of new ${}_{}{}^{145}{}_{}{}^{}\mathrm{Sm}$ levels at 2340.8, 2508.1, and 2513.0 keV. From the coincidence data, levels at 1607.6 (${\mathrm{½}}^{-}$) and 1843.6 (½, ${\frac{3}{2}}^{-}$) keV were also established; these states apparently correspond to those previously observed in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}\mathrm{}(d,p)\mathrm{}$ studies at about 1611 and 1854 keV. A survey of available data for $N=83\mathrm{}$ isotones (${}_{}{}^{137}{}_{}{}^{}\mathrm{Xe}$ → ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$) indicated a systematic shift in excitation energy for seven rather well-established single-neutron states as their location was traced from nuclide to nuclide. On this basis it was then possible to predict in ${}_{}{}^{137}{}_{}{}^{}\mathrm{Xe}$, ${}_{}{}^{141}{}_{}{}^{}\mathrm{Ce}$, and ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$ the approximate excitation energies of some of these so far unreported states.