  Method: To examine signatures of this alpha-condensation, a compound nucleus
reaction using 160, 280, and 400 MeV 16O beams impinging on a carbon target was
used to investigate the 12C(16O,7a) reaction. This permits a search for
near-threshold states in the alpha-conjugate nuclei up to 24Mg. Results: Events
up to an alpha-particle multiplicity of 7 were measured and the results were
compared to both an Extended Hauser-Feshbach calculation and the Fermi break-up
model. The measured multiplicity distribution exceeded that predicted from a
sequential decay mechanism and had a better agreement with the multi-particle
Fermi break-up model. Examination of how these 7 alpha final states could be
reconstructed to form 8Be and 12C(0_2+) showed a quantitative difference in
which decay modes were dominant compared to the Fermi break-up model. No new
states were observed in 16O, 20Ne, and 24Mg due to the effect of the N-alpha
penetrability suppressing the total alpha-particle dissociation decay mode.
Conclusion: The reaction mechanism for a high energy compound nucleus reaction
can only be described by a hybrid of sequential decay and multi-particle
breakup. Highly alpha-clustered states were seen which did not originate from
simple binary reaction processes. Direct investigations of near-threshold
states in N-alpha systems are inherently impeded by the Coulomb barrier
prohibiting the observation of states in the N-alpha decay channel. No evidence
of a highly clustered 15.1 MeV state in 16O was observed from
(28Si*,12C(0_2+))16O(0_6+) when reconstructing the Hoyle state from 3
alpha-particles. Therefore, no experimental signatures for alpha-condensation
were observed.
