Intermediate-structure fusion resonances observed in the radiative capture of /sup 12/C by /sup 12/C

We have investigated the /sup 12/C(/sup 12/C,..gamma..)/sup 24/Mg reaction, populating low-lying states of /sup 24/Mg, with /sup 12/C+/sup 12/C c.m. energies between 5 and 11 MeV. High energy ..gamma.. rays were detected in a large volume NaI spectrometer which had sufficient resolution to distinguish clearly the ..gamma../sub 0/, ..gamma../sub 1/, and ..gamma../sub 2,3/ transitions. Several resonances were observed in each of the decay channels. In particular, the ..gamma../sub 0/ excitation function has four narrow resonances at E/sub c.m./ = 5.6, 6.0, 6.8, and 8.0 MeV, which are unambiguously assigned J/sup ..pi../ = 2/sup +/. The upper three of these resonances are correlated in all three decay channels but are not correlated either with previously identified 2/sup +/ structures in the /sup 12/C+/sup 12/C system or with structure in the distribution of ground-state E2 strength in /sup 24/Mg. Furthermore, calculations demonstrate that these resonances have large nonstatistical /sup 12/C- and photon-partial widths. We argue that the data are suggestive of a new and unusual form of intermediate structure, namely highly clustered /sup 12/C+/sup 12/C configurations built on the ground-state band of /sup 24/Mg.