H. T. Duong

Hyperfine structure and isotope shift investigations in202–222Rn for the study of nuclear structure beyond Z=82

The hyperfine structure (hfs) and isotope shift (IS) in the isotopic chain of the radioactive element radon have been studied for the first time. The measurements were carried out by collinear fast-beam laser spectroscopy at the mass separator facility ISOLDE at CERN. The IS between 16 isotopes in the mass range 202≦A≦222 and the hfs of 7 odd-A isotopes were determined in the transitions 7s [3/2]2-7p [5/2]3 (745 nm) of Rn I. The nuclear spins and moments, as well as the observed inversion of the odd-even staggering for218–222Rn, can be associated with the effects of octupole instability around N=134.

Optical laser spectroscopy and hyperfine structure investigation of the 102S, 112S, 82D, and 92D excited levels in francium

The authors present an extension to low-lying states of francium (10s, 11s, 8d, 9d) of a previously published high-resolution experiment performed on the ns and nd Rydberg levels. These four levels were investigated at CERN with the on-line mass separator ISOLDE using stepwise laser excitation in collinear geometry. Accurate energy measurements lead to a more reliable determination of the quantum defects of the whole ns and nd series, together with the ionization potential for 212Fr (nuclear spin I=5) which is found to be 32848.872 (9) cm-1. The measurement of the fine structure splittings for the nd 2D3/2, 5/2 doublets was completed at the same time. The main result of the study is the first observation and measurement of hyperfine structures in 2S and 2D states.

High-resolution laser spectroscopy of Fr ns and nd Rydberg levels

The authors report on a high-resolution study of Rydberg levels in the atomic spectrum of francium, performed at CERN with the on-line mass separator ISOLDE. The ns (n=12-22) and nd (n=10-20) levels were investigated using stepwise laser excitation in collinear geometry. From these are deduced the quantum defects of the ns and nd series, as well as the ionisation potential for 212Fr: I=32848.876(7) cm-1 ( approximately=4.073 eV). This accurate value confirms and considerably improves earlier results. Owing to the high resolution of collinear laser spectroscopy, the fine-structure splittings Delta E(nd) of the nd 2D3/2, 5/2, doublets have been observed and measured for the first time. They agree with the empirical formula Delta E(nd)=Aneff-3+Bneff-5.

Bohr–Weisskopf effect: influence of the distributed nuclear magnetization on hfs

Nuclear magnetic moments provide a sensitive test of nuclear wave functions, in particular those of neutrons, which are not readily obtainable from other nuclear data. These are taking added importance by recent proposals to study parity non-conservation (PNC) effects in alkali atoms in isotopic series. By taking ratios of the PNC effects in pairs of isotopes, uncertainties in the atomic wave functions are largely cancelled out at the cost of knowledge of the change in the neutron wave function. The Bohr–Weisskopf effect (B–W) in the hyperfine structure interaction of atoms measures the influence of the spatial distribution of the nuclear magnetization, and thereby provides an additional constraint on the determination of the neutron wave function. The added great importance of B–W in the determination of QED effects from the hfs in hydrogen-like ions of heavy elements, as measured recently at GSI, is noted. The B–W experiments require precision measurements of the hfs interactions and, independently, of the nuclear magnetic moments. A novel atomic beam magnetic resonance (ABMR) method, combining rf and laser excitation, has been developed for a systematic study and initially applied to stable isotopes. Difficulties in adapting the experiment to the ISOLDE radioactive ion beam, which have now been surmounted, are discussed. A first radioactive beam measurement for this study, the precision hfs of 126Cs, has been obtained recently. The result is 3629.515(∼0.001) MHz. The ability of ABMR to determine with high precision nuclear magnetic moments in free atoms is a desideratum for the extraction of QED effects from the hfs of the hydrogen-like ions. We also point out manifestations of B–W in condensed matter and atomic physics.

Hyperfine structure and isotope shifts in heavy atoms

Measurements on the optical spectra of radioactive isotopes of heavy elements specifically thallium and bismuth are reported. Isotope shifts and hyperfine structure are measured and nuclear magnetic moments are determined. (AIP)