Collinear laser spectroscopy, radioactive

Several groups at ISOLDE are planning further improvements of their techniques. For each element the most appropriate experimental scheme has to be found. Today, collinear laser spectroscopy is the most general high-resolution and sensitive method for optical spectroscopy on radioactive beams delivered by on-line mass separators. Its sensitivity ranges from 10 - 10 atoms/s depending on the strength and multiplicity of the optical transitions. 

The first group comprises high-resolution laser spectroscopy of short-lived radioactive isotopes with lifetimes in the millisecond range. The ions are produced by nuelear reactions induced by bombardment of a thin foil with neutrons, protons, y-quanta, or other particles inside the ion source of a mass spectrometer. They are evaporated and enter after mass selection the interaction zone of the collinear laser [466]. 

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. 

Table 1. Measurements on Radioactive Nuclides by Collinear Fast-Beam Laser Spectroscopy... 

It has been shown by means of examples that the collinear laser fast-beam technique has introduced many interesting aspects into the classical field of atomic spectroscopy. This discussion has not touched upon the promising applications to molecular ions including spectroscopy and reaction studies, as the physics involved is beyond the scope of this contribution. To date, it appears that a systematic application in atomic spectroscopy has been established in the work on radioactive nuclides, owing to the sensitivity and resolution, but even more the ideal adaptation of the spectroscopic method to the conditions of production. 

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