COMPRESSION MODES: NUCLEAR INCOMPRESSIBILITY AND MICROSCOPIC STRUCTURE
Muhsin N. Harakeh (GANIL)
In the last two decades, the compression modes, the isoscalar giant monopole resonance (ISGMR) and isoscalar giant dipole resonance (ISGDR), were extensively studied, both experimentally and theoretically, because of their importance for the determination of the nuclear matter incompressibility and consequently their implications for the equation of state (EOS) of nuclear matter. A direct relationship exists between the excitation energy of the ISGMR (ISGDR) and the nuclear incompressibility, which in turn can be expressed as a sum of various terms. Though the nuclear matter incompressibility (K∞) has been reasonably well determined through comparison of experimental results on several spherical nuclei with microscopic calculations, the asymmetry term was determined with much larger uncertainties. This has been addressed in recent measurements on a series of stable Sn isotopes, which resulted in a value of Kt =-550 ± 100 MeV for the asymmetry term in the nuclear incompressibility. Furthermore, measurements of inelastic excitation of the ISGDR in coincidence with proton and neutron decay for a number of spherical nuclei revealed its microscopic structure. This is found to be in good agreement with microscopic continuum-RPA calculations. In addition, the background-free spectra that were obtained for 208Pb indicate the existence of yet another compression mode, the 4ħω overtone mode of the ISGQR.
