Isotope shift in the dielectronic recombination of three-electron ANd57+

Isotope shifts in dielectronic recombination spectra were studied for Li-like Nd-A(57+) ions with A=142 and A=150. From the displacement of resonance positions energy shifts delta E-142 150(2s-2p(1/2))=40.2(3)(6) meV [(stat)(sys)] and delta E-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)delta < 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.