Alpha-cluster Condensations in Nuclei and Experimental Approaches for their Studies

The formation of alpha-clusters in nuclei close to the decay thresholds is discussed. These states can be considered to be boson-condensates, which are formed in a second order phase transition in a mixture of nucleons and alpha-particles. The de Broglie wavelength of the alpha-particles is larger than the nuclear diameter, therefore the coherent properties of the alpha-particles give particular effects for the study of such states. The states are above the thresholds thus the enhanced emission of multiple-alphas into the same direction is observed. The probability for the emission of multiple-alphas is not described by Hauser-Feshbach theory for compound nucleus decay.Comment: 21 pages, 12 figures

Highly deformed 40^{40}Ca configurations in 28^{28}Si + 12^{12}C

The possible occurrence of highly deformed configurations in the $^{40}$Ca di-nuclear system formed in the $^{28}$Si + $^{12}$C reaction is investigated by analyzing the spectra of emitted light charged particles. Both inclusive and exclusive measurements of the heavy fragments (A $\geq$ 10) and their associated light charged particles (protons and $\alpha$ particles) have been made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding energies of $E_{lab} (^{28}$Si) = 112 MeV and 180 MeV by using the {\sc ICARE} charged particle multidetector array. The energy spectra, velocity distributions, and both in-plane and out-of-plane angular correlations of light charged particles are compared to statistical-model calculations using a consistent set of parameters with spin-dependent level densities. The analysis suggests the onset of large nuclear deformation in $^{40}$Ca at high spin.Comment: 33 pages, 11 figure

Search for cluster structure of excited states in 14C

We have studied three different 2n transfer reactions on a 12C target, the 2p pick up reaction on 16O and the 5He transfer in the reaction 9Be 7Li,d 14C. Combined with a systematic search through experimental results for transfer reactions, inelastic excitations and other data, we have established an almost complete spectroscopy for 14C up to 18 MeV excitation. We identify states with single particle structure that have oblate shapes and states corresponding to proton excitations that are connected to oblate triangular cluster states. Further we list states of prolate shape which have no simple structure related to the low lying oblate states of 12C. These are proposed to have strong clustering and to form rotational bands as a parity inversion doublet, with high moment of inertia. With these results it is possible for the first time to identify chain states expected in the isotope 14