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Total nuclear reaction cross-sections are determined by means of a 4 re-7 method. The results cover a wide span of targets for various stable beams. The validity of the method is shown in a combined systematics including also the results of transmission-type experiments. The data are very well described by the formula developed by Kox et al. The same method is applied to secondary fragment beams produced from a 44 MeV/u 22Ne beam on a 332 mg/cm 2 181Ta target. Using the LISE spectrometer the fragments 4'6He, [6][7][8][9][7][8][9][10][11][12] are analyzed and transported to interact with a 199.4 mg/cm 2 Cu target surrounded by a 4rc-7 counter. The measured total reaction cross-sections oR are discussed in terms of the reduced strong absorption radius ro and compared with other experimental results.

AbstracL Resonance ionization spectroscopy in collinear geometly has been successfully applied to a fast beam of ytterbium atoms. The atoms were excited stepwise into a Rydberg state by pulsed laser lighl, ionized in an electrical field and deflected onlo a secondaty electron detector. The efficiency was 1 x lo-' delecled ions per incoming atom an a background from collisional ionization of 1 x 10V8. The technique has been exploited for 1he measurement of hyperfine structures and isotope shifls of unstable ytterbium isotopes, in particular IS7Yb, lS9Yb and 17rYb.

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