Changes in the mean square charge radii of neutron-deficient europium isotopes measured by the laser ion source resonance ionization spectroscopy

The laser ion source has been used for the study of the isotope shifts of neutron-deficient Eu isotopes. The extension of the region of applicability of the method by using the γ - and β -radiation detection is reported. We have measured the isotope shifts of the europium optical line 576.520 nm for 137-139,141,142m,143,144Eu. To increase the laser ion source efficiency an axial magnetic field (350 gauss) was applied. Nearly a twofold rise of the ionization efficiency for Eu was observed. By using the effect of optical ion bunching an increase of the selectivity was obtained. The isotope shift data for 139,141,142m,143,144Eu are in agreement with the previously measured isotope shifts for these nuclides. The new data for 137Eu and refined data for 138Eu point to a gradual increase of the deformation for these isotopes. Comparisons with microscopic-macroscopic calculations and calculations in the framework of the Hartree-Fock model were performed. (orig.)