Nuclear excitation by electron capture (NEEC) is a coupled nuclear-atomic process by which the capture of an electron by an ion into an atomic vacancy results in the excitation of the corresponding nucleus into a higher excited state. To date, there has been only one experimental result, for the nucleus ${}^{93}\mathrm{Mo}$, where a signal indicative of NEEC has been reported. Additional experimental data are vital to provide a testbed for developing theoretical NEEC models to aid in better understanding this phenomenon. In this work, a second NEEC candidate, ${}^{127}\mathrm{Cs}$, was explored using a methodology similar to that in the prior ${}^{93}\mathrm{Mo}$ study. Highly stripped ions of ${}^{127}\mathrm{Cs}$ in its 53.3-$\mu \mathrm{s}$ isomeric state were produced in ${}^9\mathrm{Be}({}^{123}\mathrm{Sb},5n)$ reactions and implanted into target foils. NEEC-signature $\gamma$-ray coincidences were sought using the Digital Gammasphere spectrometer. Although a signature was not observed, upper limits on the NEEC probability were established: 0.17% for implantation into a layered ${}^{27}\mathrm{Al}/{}^{208}\mathrm{Pb}$ target and 0.27% for a single ${}^{208}\mathrm{Pb}$ foil. Theory predicts a yield well below these levels; while the results for ${}^{127}\mathrm{Cs}$ are thus consistent, they ultimately do not provide an explanation that helps resolve the underlying discrepancy between theory and experiment for ${}^{93}\mathrm{Mo}$.

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• Electromagnetic transitions
• Electron & muon capture
• Fusion evaporation reactions
• Nuclear structure & decays
• 90 ≤ A ≤ 149
• Spectrometers & spectroscopic techniques