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Isotope shifts and hyperfine splittings in optical transitions for atomic ions of the thorium isotopes227Th to230Th and232Th have been measured by laser spectroscopy on stored ions. From the isotope shift data, changes of the mean square charge radii are determined. A continuous increase of the charge radius with mass numberA is observed, in agreement with droplet model calculations. The results indicate that the odd-even staggering for Th is different from that one of the neighbouring isotones of Fr and Ra. There is some empirical evidence from systematics for an inversion of the staggering and the appearance of an octupole deformation atN ≦137. The hyperfine splitting for229Th for 3 electronic levels is given.

The isotope shifts and hyperfine splittings for 11 strontium isotopes (A=80–90) and two isomers for the optical transition λ=293.2 nm were measured. The magnetic dipole and electric quadrupole moments and the changes of the mean square charge radii are derived. The results are discussed with respect to the increasing nuclear deformation and the anomalous coupling scheme of light Sr nuclei.

The hyperfine structure of Am atoms was investigated in an atomic beam by laser spectroscopy. The observed splittings were evaluated with respect to the magnetic dipole and electric quadrupole moments of242mAm. The results are: μ I (242mAm)=+0.97(5)nm,Q(242mAm)=+6.5(2.0)b.