High-resolution laser spectroscopy on the hyperfine structure and isotope shift of 237,239 Np

Nuclear ground state properties of 237,239 Np were investigated by high-resolution laser spectroscopy at the RISIKO mass separator off-line radioactive beam facility of the University of Mainz. The isotope shifts and the hyperfine parameters were determined in two different atomic ground-state transitions at 398.80 nm and 395.61 nm. The data allowed for calculation of the so far unknown nuclear moments of the short-lived isotope 239 Np, i.e. the nuclear magnetic dipole moment of μI = +3.18(2) μN and the electric quadrupole moment of Q S = +4.05(8) eb, using the known nuclear moments of 237 Np as a reference, which were determined by electron paramagnetic resonance and investigations of muonic X-ray hyperfine structures, respectively.