Abstract.We have used an optical pumping-Zeeman scanning technique in order to determine the isotope shift in the 3,261 A resonance line of 43-day, spin-ll/2 l~SmCd. A sample of ~ 5 x 10 ~2 atoms was aligned in the IS 0 diamagnetic ground state by optically pumping the sample with one selected Zeeman-scanned component of the 3P a -3,261 A resonance line from a 11~Cd lamp. The alignment was detected through the modulation of the pumping beam at the nuclear resonance frequency. Thus by Zeeman scanning the F = 9/2 component of the 3P 1 level and using previously determined A-and B-values, we find 6v(l14-115m(9/2))= -4,234(48)MHz and t~4Cd-atsmCd isotope shift=87(48)MHz. We calculate a staggering parameter ?(ltS~Cd)=0.73(26), and a change in mean-square nuclear charge radius 6 (r2) 114' 115m =0.035 (18) fm 2.