On the interplay between giant resonances and background

The problem of extracting spectroscopic strength from a resonance with fine-structure components, arising from underlying levels, is investigated in the framework of the continuum shell model. It is shown that the underlying levels are correlated strongly at the top of resonances due to the unitarity of the S matrix. This selective non-statistical behaviour of the underlying levels leads to missing spectroscopic strength in the traditional methods of analysing the data and to a selective transparency at the top of resonances. (author)