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Background: Near-threshold α-clustered states in light nuclei have been postulated to have a structure consisting of a diffuse gas of α-particles which condense into the 0s orbital. Experimental evidence for such a dramatic phase change in the structure of the nucleus has not yet been observed. Method:To examine signatures of this α-condensation, a compound nucleus reaction using 160, 280, and 400 MeV 16 O beams impinging on a carbon target was used to investigate the 12 C( 16 O, 7α) reaction. This permits a search for near-threshold states in the α-conjugate nuclei up to 24 Mg.Results: Events up to an α-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 7α final states could be reconstructed to form 8 Be and 12 C(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 16 O, 20 Ne, and 24 Mg due to the effect of the N-α penetrability suppressing the total α-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 α-clustered states were seen which did not originate from simple binary reaction processes. Direct investigations of near-threshold states in N-α systems are inherently impeded by the Coulomb barrier prohibiting the observation of states in the N-α decay channel. No evidence of a highly clustered 15.1 MeV state in 16 O was observed from ( 28 Si , 12 C(0 + 2 )) 16 O(0 + 6 ) when reconstructing the Hoyle state from 3 α-particles. Therefore, no experimental signatures for α-condensation were observed. arXiv:1907.05471v2 [nucl-ex]

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The TexAT (Texas Active Target) detector is a new active-target time projection chamber (TPC) that was built at the Cyclotron Institute Texas A&M University. The detector is designed to be of general use for nuclear structure and nuclear astrophysics experiments with rare isotope beams. TexAT combines a highly segmented Time Projection Chamber (TPC) with two layers of solid state detectors. It provides high efficiency and flexibility for experiments with low intensity exotic beams, allowing for the 3D track reconstruction of the incoming and outgoing particles involved in nuclear reactions and decays.

Two recent experiments have indicated that the break-up of the 12C Hoyle state is dominated by the sequential 8Be(g.s.) + α decay channel. The rare direct 3α decay was found to contribute with a branching ratio of less than 0.047% (95% C.L.). However, the ability of experimentalists to successfully disentangle these two competing decay channels relies on accurate theoretical predictions of how they each manifest in phase space distribution of the three break-up α-particles. The following paper reviews the current theoretical approaches to calculating the break-up of the Hoyle state and introduces a semi-classical WKB approach, which adequately reproduces the results of more sophisticated calculations. It is proposed that a more accurate upper limit on this branching ratio may be obtained if these new theoretical results are taken into account when analysing experimental data.