Laser-induced fluorescence spectroscopy in a collimated atomic beam has been applied to determine isotope shifts and the hyperfine structure of an isotopic chain of the radioactive element polonium (' Po, 202Po, '0 ' Po). The relative isotope shifts show a striking similarity with results for other elements in the vicinity of Pb, even reproducing details of the odd-even staggering.Optical spectroscopy, in particular, highly sensitive laser-spectroscopic methods, have proven to be a powerful tool for investigations of nuclear ground-state properties through measurements of isotope shifts and hyperfine structure in atomic spectra [1]. In heavy elements, isotope shifts directly reflect, to a large extent, the variations in the mean-square radius (r ) of the nuclear charge distribution. From the point of view of nuclear structure interest, this is advantageous and is in contrast to the situation found for medium-mass nuclei where the uncertainties of mass-dependent effects (due to many-electron correlations) may obscure the nuclear information. Thus, systematic studies of relative isotope shifts in neighboring heavy elements may provide a basis for isotopic and isotonic comparisons, i.e. , of studies of the nucleon rearrangement when neutrons and protons are added or removed. In this aspect the region in the vicinity of the doubly magic nucleus Pb (Z =82, N=126) has attracted considerable attention following the observation of a sudden change of the nuclear deformation in light Hg isotopes [2] with subsequent investigation of Au (Ref. [3]) and Pt (Ref. [4]) nuclei.Nevertheless, there appears to be a conspicuous lack of experimental information for elements with Z )82, such as Bi, Po, and At, which would allow interesting comparisons of the nuclear structure before and after closing of shells. This situation has prompted the present laser-spectroscopic studies of polonium isotopes for which experimental data on isotope shifts and nuclear radii were completely missing, and the knowledge on electromagnetic moments of the ground state is scarce.The measurements are based on the observation of resonance fluorescence after excitation of the atomic transition 6p P2 6p 7s S2 of Po I in a collimated atomic beam. The required ultraviolet light (A, =255.8 nm) was generated in a Coherent-type 699 cw ring dye laser with intracavity frequency doubling (Fig. 1). The dye laser was operated with Coumarin 498 at k =511. 6 nm; it was optically pumped by the 457.9-nm line of an argon-ion laser at a power of about 1.5-2.2 W. Because of the low pump power available, the internal losses of the dye laser cavity had to be reduced. For this purpose the mode selecting intracavity assembly was removed from the laser and replaced by two almost "lossless" uncoated etalons of 2 mm and 0.5 mm thickness [5].A P-barium borate crystal [6] (5 mm length) was used for frequency doubling; its entrance and exit faces were laser fluorescence & computerf requency intensity iodine j spectrum
We present new measurements of isotopic shifts and hyperfine structure in the lead resonance line for a total of 15 isotopes. The experimental accuracy is of order 4 MHz. Using independent measurements of the nuclear parameter A for the stable isotopes we have derived A for all measured isotopes.
The isotope shift and hyperfine structure of the optical Sn resonance transition 5p 2 3 p 0 -+ 5p6s 3 P 1 at >..=286.3nm have been studied for 18 Sn nuclei including 2 isomers. Laser induced resonance fluorescence from a collimated atomic beam of tin was observed using a tunable cw dye Iaser .with frequency doubler. The electromagnetic nuclear moments and changes of the mean square charge radii of the nuclear charge distributions were determined. The results are discussed with respect to the information they provide on the nuclear structure of the nuclei investigated; they are compared with various theoretical models.
DIE LASERSPEKTROSKOPISCHE BESTIMMUNG DER KERN-LADUNGS-RADIEN UND -MOMENTE VON ZINN-ATOMKERNEN
I. I ntroductionThe energies of atomic transitions, in particular those associated with s electrons, alter slightly with the neutron number of the atomic nucleus. This isotope shift arises from the difference of the nuclear masses of the isotopes and from the difference of the nuclear Coulomb field experienced by the atomic electrons involved in the transition. The latter contribution, historically referred to as volume effect, 1 is due to isotopic differences of the nuclear charge distributions of which the mean square eh arge radius
Isotope shifts and hyperfine splittings in optical transitions for atomic ions of the thorium isotopes 227Th to 23~ and 232Th 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 number A 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 at N< 137. The hyperfine splitting for 229Th for 3 electronic levels is given.
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