Laser Spectroscopy of Short-Lived Isotopes in Fast Atomic Beams and Resonance Cells

Abstract

The introduction of laser techniques to optical spectroscopy of hyperfine structure (HFS) and isotope shift (IS) has put new life into this field at the intersection between atomic and nuclear physics which is now about fifty years old. Two severe limitations of classical spectroscopy could be reduced drastically, i.e., (i) the amount of atoms needed for optical spectroscopy and (ii) the Doppler width of optical lines. The increase in sensitivity went together with the development of powerful accelerators or reactors so that exotic nuclei with half lives down to 10 msec can now be produced and optically analysed. The increase in resolution allows the determination of nuclear spins, nuclear moments, and changes of charge radii between different isotopes even for very low Z nuclei. In the case of the measurement of spins and moments, optical spectroscopy has to compete with very elaborate atomic and nuclear spectroscopic methods as, e.g., the atomic beam magnetic resonance, optical rf techniques or γ spectroscopy. However, only optical spectroscopy gives access to the nuclear-volume dependent IS of short-lived isotopes which provides a very sensitive measure of the radial change when the neutron number is varied. It is this information that turned out to be very fruitful as will be shown or the case of Hg isotopes. This is because the radial change in an isotopic chain reflects collective as well as single particle effects, namely the gross behaviour of an expanding nucleus when neutron are added as compared to the standard and generally used A1/ 3 law (so called IS discrepancy), the effect of the addition of a single neutron or a neutron pair (odd-even staggering), the influence of the orbit of different unpaired neutrons (isomer shift), and changes in the nuclear shape (deformation effect).