EXACT AND APPROXIMATE CALCULATION OF GIANT-RESONANCES

Energies, sum rules and partial decay widths of giant resonances in Pb -208 are calculated solving exactly the continuum RPA equations corres ponding to a central Woods-Saxon potential. For comparison an approxim ate treatment of those quantities in terms of pole expansions of the G reen function (Berggren and Mittag-Leffler) is also performed. It is f ound that the approximated results agree well with the exact ones. Com parison with experimental data is made and a search for physically mea ningful resonances is carried out.