Interfering states and narrow resonances at high excitation energy

Abstract

A schematic model of multipole giant resonances is considered which treats the external interaction of the resonance states via common decay channels on the same footing as the internal residual interaction. At high excitation energy, the cross-section pattern is governed by the phenomenon of resonance trapping, i.e. by the formation of different time scales. The interplay of internal and external collectivity influences significantly the distribution of the dipole strengths over the single states as well as their widths and positions in energy. A realistic calculation is performed for208Pb. The strength function of the 4ℏω isoscalar monopole giant resonance is obtained in the framework of the random phase approximation in the continuum. The oneparticle continuum is shown to play an important role in the formation of the structure of the strength function. Some narrow resonances appear due to resonance trapping.