Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in At-217,At-218,At-219 revealed by in-source laser spectroscopy

Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in At-217,At-218,At-219 have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope At-218 has been found to be larger than the average of its even-N neighbors, At-217,At-219. The discrepancy between the additivity-rule prediction and experimental data for the magnetic moment of At-218 also supports the possible presence of octupole collectivity in the considered nuclei.