Alpha-particle clustering in self-conjugate nuclei from the experimental side

The fragmentation of quasi-projectiles from the nuclear reaction ^40 Ca+ ^12 C at 25 MeV per nucleon bombarding energy was used to produce excited self-conjugate nuclei (from ^16 O to ^28 Si). Temperature and density conditions for alpha-clustering were determined. Measured temperatures have been found in the range of 5.5 - 6.0 MeV whereas density values of 0.3 - 0.4 times the saturation density are deduced. This density domain is also predicted by constrained self-consistent mean field calculations. At present such calculations are performed at zero temperatures and geometric alpha cluster configurations are observed: a tetrahedron for ^16 O for example. Experimentally, by looking to ^8 Be production from excited self-conjugate nuclei, a signature of final state interaction between two alpha-particles was evidenced. This indicates that, due to the temperature, geometric configurations are not the only ones present, which argues in favor of finite temperature calculations.