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Description
This study aims to investigate the effects of the octupole vibrations on the fine structure of the isoscalar giant monopole resonance (ISGMR) in 208Pb. Quasi-Particle Model (QPM) based on the Skyrme Energy Density Functional approach was applied to allow for disentangling the origin of damping mechanisms beyond Random Phase Approximation (RPA) for this heavy doubly-magic nucleus. ISGMR was excited in the 208Pb target nucleus using alpha-particle inelastic scattering measurements acquired with an E_α = 196 MeV beam at zero-degree scattering angle. iThemba LABS K600 magnetic spectrometer was used to detect and momentum-analyze the inelastically scattered alpha particles. An experimental energy resolution of ~70 keV (FWHM) was achieved, revealing fine structure in the excitation-energy region of the ISGMR. Experimental and theoretical isoscalar strength functions for 208Pb were extracted and compared using a wavelet analysis technique. The obtained power spectra and the characteristic energy scales showed that an extension of the two-phonon space allowing for octupole phonons substantially enriches the spectrum of the energy scales.