Eliseev, S., Roux, C., Blaum, K., Block, M., Droese, D., Herfurth, F., et al. (2011). Resonant Enhancement of Neutrinoless Double-Electron Capture in 152Gd. Physical Review Letters, 106(5): 052504, pp. 1-4. doi:10.1103/PhysRevLett.106.052504.