KALLEN-SABRY ENERGY SHIFT FOR HYDROGEN-LIKE ATOMS WITH FINITE-SIZE NUCLEI

The vacuum polarization potential of order alpha2(Zalpha) is evaluated numerically for elements with 1 less-than-or-equal-to Z less-than-or- equal-to 100. The finite size of nuclei is taken into account. The nuc lear charge distribution is described by a homogeneously charged spher e. We compare the resulting energy shift for finite size nuclei with p oint nucleus values and find a maximum effect of 0.1 eV for K-shell el ectrons in Fm-100, which represents an 8% modification. This nuclear s ize effect might be of relevance for future Lamb-shift measurements.