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Study of exotic resonances

The nuclear structure group is planning an ambitious research programme in the field of giant resonances. The isoscalar giant monopole resonance gives access to the modulus of incompressibility of nuclear matter. The extension of its study to long isotopic chains will allow probing of the isospin dependence of incompressibility. Pygmy dipole resonances, new dynamic modes notably associated with an excess of neutrons far from stability, have a strong influence on the radiative capture reaction rate involved in the r-process. Moreover, their study allows the thickness of neutron skins to be evaluated or the symmetry energy parameters to be extracted. Similarly, certain spin-isospin modes, such as dipole spin resonance, can be highlighted. A programme has been undertaken at GANIL with the MAYA detector, in which giant monopole and quadrupole resonances have been measured for the first time in far from stability, in the 56Ni and 68Ni nuclei. In addition to this programme being pursued at GANIL with the new ACTAR detector, other exotic modes can be studied at RIKEN then at FAIR, which have ideal beam energies for these studies. Last, we ought to mention the research into giant pairing vibration, which has been predicted for a long time although never observed and was recently the subject of experiments at LNS Catania. This experimental work on collective modes is carried out in close collaboration with the efforts of the theory group in the description of these modes and their link to modulus of incompressibility and symmetry energy (giant and pygmy resonances, pairing vibrations, etc.) : see Figures 1 and 2.

Figure 1 : Monopole response of pair-pair nuclei of the isotopic chain of Ni calculated with the RQRPA model (E. Khan, N. Paar, D. Vretenar, Phys. Rev. C 84 051301, 2011)

Figure 2 Monopole response B(E(0) (e2fm4) of the 16O nucleus as a function of the excitation energy (MeV) calculated with the RPA and the second RPA (SRPA)



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