MEASUREMENTS OF ISOTOPE SHIFT IN EU-II

The isotope shift between singly-charged Eu-151 and Eu-153 in the 4f(7 )(S-8 degrees)6s S-9 degrees(4) - 4f(7)(S-8 degrees)6p(1/2) J = 4 tran sition at 4129 Angstrom has been measured using fast ion beam-laser te chnique. This Eu line has attracted interest in connection with effort s of obtaining a cosmochronometer based on observed Th/Eu abundance ra tios. Knowledge of the isotope shift is of importance in order to chec k that contaminations from line blends do not contribute to the line i ntensity of Eu II. The measured value of the isotope shift -0.1527 (2) cm(-1) is consistent with the old spectroscopic value of Krebs and Wi nkler (-0.1503 (25 )cm(-1)) using a Fabry-Perot interferometer, while the accuracy is improved substantially.