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.

Mass measurements of fission and projectile fragments, produced via 238 U and 124 Xe primary beams, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the Fragment Separator (FRS) Ion Catcher with a mass resolving power (FWHM) of up to 410 000 and an uncertainty of down to 6 × 10 −8. The nuclides were produced and separated in flight with the fragment separator FRS at 300 to 1000 MeV/u and thermalized in a cryogenic stopping cell. The data-analysis procedure was developed to determine with highest accuracy the mass values and the corresponding uncertainties for the most challenging conditions: down to a few events in a spectrum and overlapping distributions, which can be distinguished from a single peak only by a broader peak shape. With this procedure, the resolution of low-lying isomers is increased by a factor of up to 3 compared to standard data analysis. The ground-state masses of 31 short-lived nuclides of 15 different elements with half-lives of down to 17.9 ms and count rates as low as 11 events per nuclide were determined. This is the first direct mass measurement for seven nuclides. The excitation energies and the isomer-to-groundstate ratios of six isomeric states with excitation energies of as little as 280 keV were measured. For nuclides with known mass values, the average relative deviation from the literature values is (4.5 ± 5.3) × 10 −8. The measured two-neutron separation energies and their slopes near and at the N = 126 and Z = 82 shell closures indicate a strong element-dependent binding energy of the first neutron above the closed proton shell Z = 82. The experimental results deviate strongly from the theoretical predictions, especially for N = 126 and N = 127.

Proton radii of 12−19 C densities derived from first accurate charge changing cross section measurements at 900A MeV with a carbon target are reported. A thick neutron surface evolves from ∼ 0.5 fm in 15 C to ∼ 1 fm in 19 C. The halo radius in 19 C is found to be 6.4±0.7 fm as large as 11 Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce well the radii.

The first measurement of the momentum distribution for one-neutron removal from (24)O at 920A MeV performed at GSI, Darmstadt is reported. The observed distribution has a width (FWHM) of 99 +/- 4 MeV/c in the projectile rest frame and a one-neutron removal cross section of 63 +/- 7 mb. The results are well explained with a nearly pure 2s_{1/2} neutron spectroscopic factor of 1.74 +/- 0.19 within the eikonal model. This large s-wave probability shows a spherical shell closure thereby confirming earlier suggestions that (24)O is a new doubly magic nucleus.

The very neutron-rich oxygen isotopes 25