Spectroscopy on Unstable Isotopes

It may be surprising to find the most extensive application of collinear laser fast-beam spectroscopy in a field that a priori has little connection with the special features of this technique. Neither the Doppler shift nor the accessibility of ionic spectra plays a decisive role for the on-line experiments on radioactive isotopes from nuclear reactions. However, most of the problems encountered in the preparation of a sample of free atoms (cf. Part B, Chapter 17 by H.-J. Kluge) are solved by a combination of the fast-beam technique with the well-established concept of on-line isotope separation. The isotope separators (with ISOLDE at CERN as an outstanding example) provide the unstable species in the form of ion beams whose phase-space volume is well matched to the requirements of collinear spectroscopy. 

Obvious advantages allow the investigation of nearly any element which is available from the isotope separator  

The sensitivity, owing to efiBdent excitation within the narrow Doppler profile, is essential for the low production rate of isotopes far from stability. 

The Doppler effect provides a large tuning range and easy control of the effective wavelength of the laser light. 

Fluorescence detection gives the greatest versatility, and specialized particle detection schemes may further improve the sensitivity. The high resolution yields sufiiciently accurate hyperfine structure parameters and isotope shifts. 

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