Calibration of the isomer shift of129I

Radioactive^129mTe was implanted in 6 different transition metals (V, Fe, W, Au, Pt, Pb) and internal conversion electron spectra as well as Mössbauer spectra of the daughter nucleus¹²⁹I were measured. A value (r ²)=+1.8(4)×10^–2 fm² (corresponding to R/R=+4.1(10)×10^–4) was derived for the change of the mean square charge radius during the 27.8 keV transition in¹²⁹I. The consequences of this measurement on the calibration constants of the Mössbauer isomer shifts of other isotopes of the 5sp elements are discussed.