Search for the 6α condensed state in 24Mg using the 12C+12C scattering
Abstract
We searched for the 6α-condensed state in 24Mg by measuring the 12C+12C scattering with the SAKRA Si detector array at Ecm = 17.5-25.0 MeV. By using the invariant-mass method for the detected 3α particles, the inclusive cross sections for the 12C+12C12C(0+2)+X and 12C(3-1)+X reactions were determined. In addition, the missing-mass spectroscopy was successfully utilized to determine the excitation energy of the residual 12C nucleus and the exclusive cross sections for the 12C+12C12C(0+2)+12C(0+1), 12C(0+2)+12C(2+1), and 12C(0+2)+12C(0+2) reactions. In both the inclusive 12C(0+2)+X channel and the exclusive 12C(0+2)+12C(0+1) channel, the cross section peaked at Ermcm = 19.4 MeV, which correspond to the excitation energy of Ex = 33.3 MeV in 24Mg. This 19.4-MeV state is a candidate for the 6α-condensed state because of the agreement of the excitation energy with the theoretical value and its decay property. In the exclusive 12C(0+2)+12C(0+2) channel, a broad state was observed at Ecm = 22.5 MeV, which correspond to the excitation energy of Ex = 36.4 MeV in 24Mg. From the angular distribution of the differential cross section, the spin and parity of this 22.5-MeV state was assigned to be 4+. In addition, a 2+ state was suggested at the low-energy side of the 22.5-MeV state. Because their excitation energies are higher than the theoretical value of the 6α-condensed state, these states might be excited states of the 6α-condensed state such as the 2+2 and 4+1 states in 12C.
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