Structure of the isoscalar giant quadrupole resonances (GQR) IN 12C, 160, 28Si, fragmentation of the E2-strength ian light nuclei and the importance of a blocking mechanism for the GQR in 13C.

Abstract

The existence of a strong fragmented GQR in light nuclei is commonly accepted~. The theoretical explanation of this effect has been established by the coupling of the (Iplh) excitations with more complex configurations, like, e.g. the (2p2h)-states. In fig. 1 we present (Ip~h + 2p2h) RPA-calculations for the isoscalar GQ~ in ~C, ~60 and a8 Si in the frame of the MSI model 2~ . Whereas in a (~pWh) calculation the E2-strength is concentrated for all three nuclei in nearly one state, the inclusion of the (2p2h) states leads to a strong splitting of the E2-strength distribution. To find out the underlying structure responsible for the specific aspects of the GQR in light nuclei, we calculated the energy averaged spectroscopic factors of the relevant (Iplh)-configurations (~) of the GQR in the resonance region C~(~) : ~/~ ~i l~ where N denotes ~: