Abstract
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.
Purpose: To understand the role of α condensation in light nuclei experimentally.
Method: To examine signatures of this α 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,7α) reaction. This permits a search for near-threshold states in the α-conjugate nuclei up to 24Mg.
Results: Events up to an α-particle multiplicity of seven were measured and the results were compared to both an extended Hauser-Feshbach calculation and the Fermi breakup model. The measured multiplicity distribution exceeded that predicted from a sequential decay mechanism and had a better agreement with the multiparticle Fermi breakup model. Examination of how these 7α final states could be reconstructed to form 8Be and 12C(02+) showed a quantitative difference in which decay modes were dominant compared to the Fermi breakup model. No new states were observed in 16O, 20Ne, and 24Mg 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 multiparticle 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 16O was observed from [28Si★, 12C(02+)] 16O(06+) when reconstructing the Hoyle state from three α particles. Therefore, no experimental signatures for α condensation were observed.
Original language | English |
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Article number | 034320 |
Number of pages | 20 |
Journal | Physical Review C |
Volume | 100 |
Issue number | 3 |
DOIs | |
Publication status | Published - 20 Sept 2019 |
ASJC Scopus subject areas
- Nuclear and High Energy Physics