DETERMINATION OF NUCLEAR QUADRUPOLE MOMENTS OF 2 STABLE EUROPIUM ISOTOPES FROM EU 2-SPECTRUM

The hyperfine structure of the transitions 4 f7 6 p9P3,4,5-4 f7 6 s9S4,7S3 in the spark spectrum of europium was investigated by a digital recording double-Fabry-Perot-spectrometer. Enriched samples of151Eu and153Eu were used in hollow cathode light sources cooled in liquid air. As the hyperfine splitting of the9P levels was not completely resolved the patterns were analysed by a computer. The A- and B-values of the9P levels were determined for both isotopes. Together with the experimental A-values of the7P levels these A-values were used to check the eigenfunctions of Bordarier, Judd, and Klapisch, which have been calculated for intermediate coupling. Good agreement between observed and calculated A-values was reached only if the spherical-symmetric part of the magnetic hyperfine interaction operator of the 6 p-electron was used as a free parameter. In this way the configuration interaction between 4 f7 6 p and 4 f6 6 s 6 d can be taken into account. Fortunately this mixing does not affect the quadrupole interaction. Therefore the quadrupole moments were derived from the measured B-values using the unperturbed eigenfunctions. The results Q(151Eu)=(1.12 ±0.07) · 10-24 cm2 and Q(153Eu)=(2.85 ± 0.18) · 10-24cm2 are in complete agreement with the values obtained by Müller, Steudel, and Walther in the 4f7 6 s 6 p levels of the arc spectrum of europium. The values found for the hyperfine anomaly agree very well with the values derived from levels in Eu I and Eu III. © 1968 Springer-Verlag.