J.L. Vialle

Hyperfine structure and isotope shift of the D2 line of 118–145Cs and some of their isomers

Abstract High-resolution laser spectroscopy has been performed on 118–145 Cs and 119m, 121m, 122m, 130m, 134m, 135m, 136m, 138m, Cs.The Cs nuclei have been produced either by spallation of La or by fission of U by the 600 MeV proton beam, from the SC at CERN. The hyperfine structures, spins, and isotope shifts have been measured. The charge radii changes deduced from the isotope shifts exhibit shell effects at N = 82, isomeric staggering for N = 64,66,67 and a strong odd-even staggering for all isotopes with N

High-resolution laser spectroscopy on the D1 and D2 lines of 39,40,441K using RF modulated laser light

Two natural polyisotopic potassium beams were illuminated respectively by a RF modulated and an unmodulated laser beam. The laser side band frequency is locked on an atomic frequency, while the unmodulated laser frequency is RF scanned. The RF accuracy of the frequency scale allows measurements to about 0.3 MHz of the hyperfine structures and the isotope shifts of the D1 and D2 lines of 39,40,41K. The results obtained are reported and compared to the previous ones.

Field ionisation study of high lying Rydberg states of Na

The authors describe the details of an experiment using a sodium atomic beam and two dye lasers. By stepwise excitation they have selectively populated highly excited ns, nd and, using Stark mixing, np states fron n=20-50. The excited atoms were detected by field ionisation. The results obtained for the ionisation threshold fields for these states are presented and compared with the theoretical classical law Fc=(2n*)-4. A suitable field shape and detection technique allows the observation of multiple thresholds with high sensitivity. Multiple thresholds for nd states have been observed, as expected. Some ns singlet states also show multiple thresholds. Using suitably polarised laser beams the mod mL mod dependence of the ionisation threshold fields for the 20d state has been observed. The approach proposed recently by Gallagher for predicting the threshold fields is generally confirmed.

Experimental separation and study of the two partial photoionisation cross sections σ3p,s and σ3p,d from the 3p state of sodium

The two partial photoionisation cross sections sigma 3p,s and sigma 3p,d from the 3p state of Na were measured separately using an atomic beam of sodium and two appropriately polarised light sources. The observed variations of the two partial cross sections with the wavenumber of the photoionising light in the range 24000-29000 cm-1 above threshold are compared with earlier theoretical results.

Accurate wavenumbers of the first resonance doublet of francium atoms and relativistic contribution to isotope shifts in the resonance doublets of francium and caesium atoms

The results of a new experiment using high-resolution Doppler-free laser spectroscopy are reported. Firstly, the wavenumbers of the D1 and D2 lines of Fr atoms have been accurately measured: sigma (D1)-12237.409 (2) cm-1 and sigma (D2)=13923.998 (2) cm-1. Secondly, the isotope shifts of the D1 and D2 lines have been compared for Fr and Cs atoms. The contribution of the p1/2 electron to the volume shift has been measured relative to that of the s1/2 electron as 4.75(25)*10-2 for Fr and 1.4(3)*10-2 for Cs. They are discussed in terms of semi-empirical calculations as well as relativistic Dirac-Fock ones.

Hyperfine Spectroscopy of Radioactive Alkali Isotopes

Systematic experimental studies of long series of radioactive isotopes of the same element are now becoming a rapidly developing area. The results obtained in the case of Hg isotopes for instance [1], give a good idea of the attractiveness of such a type of investigation. Moreover, similar studies of radioactive Na isotopes of mass number 21 to 31 have already been performed using high resolution laser spectroscopy [2], and have shown for the first time for such a light element, an appreciable volume shift contribution to the total isotope shift. Obviously, hyperfine results, as well as nuclear spin determinations and precise isotope shift measurements give an ensemble of data that seem to be of crucial importance to a better understanding of nuclear properties and suggest new refinements in theoretical models. The further the isotopes are from magic numbers, the larger the nuclear deformations are expected to be. One has therefore to deal with essentially short-lived species, which requires one to work on-line behind the accelerators where they are produced. In the previously mentioned case of Na atoms for instance, the nuclei were obtained by fission reactions of uranium targets bombarded by 20 GeV protons delivered by the PS synchrotron of C.E.R.N..