We report on time-modulated two-body weak decays observed in the orbital electron capture of hydrogenlike 140 Pr 59+ and 142 Pm 60+ ions coasting in an ion storage ring. Using non-destructive single ion, time-resolved Schottky mass spectrometry we found that the expected exponential decay is modulated in time with a modulation period of about 7 seconds for both systems. Tentatively this observation is attributed to the coherent superposition of finite mass eigenstates of the electron neutrinos from the weak decay into a two-body final state.

Isotope shifts in dielectronic recombination spectra were studied for Li-like A Nd 57+ ions with A=142 and A=150. From the displacement of resonance positions energy shifts δE 142,150 (2s − 2p 1/2 ) = 40.2(3)(6) meV ((stat)(sys)) and δE 142,150 (2s − 2p 3/2 ) = 42.3(12)(20) meV of 2s − 2p j transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of 142,150 δ r 2 = -1.36(1)(3) fm 2 . The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size.

We report the observation of an interference between the electric dipole (E1) and the magnetic quadrupole (M2) amplitudes for the linear polarization of the Ly-α1 (2p3/2→1s1/2) radiation of hydrogenlike uranium. This multipole mixing arises from the coupling of the ion to different multipole components of the radiation field. Our observation indicates a significant depolarization of the Ly-α1 radiation due to the E1-M2 amplitude mixing. It proves that a combined measurement of the linear polarization and of the angular distribution enables a very precise determination of the ratio of the E1 and the M2 transition amplitudes and the corresponding transition rates without any assumptions concerning the population mechanism for the 2p3/2 state.