Background: Near-threshold alpha-clustered states in light nuclei have been postulated to have a structure consisting of a diffuse gas of alpha 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 alpha condensation in light nuclei experimentally.Method: To examine signatures of this alpha condensation, a compound nucleus reaction using 160-, 280-, and 400-(MeVO)-O- 16 beams impinging on a carbon target was used to investigate the C-12(O-16, 7 alpha) reaction. This permits a search for near-threshold states in the alpha-conjugate nuclei up to Mg-24.Results: Events up to an alpha-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 7 alpha final states could be reconstructed to form Be-8 and( 12)C(0(2)(+)) showed a quantitative difference in which decay modes were dominant compared to the Fermi breakup model. No new states were observed in O-16, Ne-20, and Mg-24 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 multiparticle 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 O-16 was observed from [Si-28 *, C-12(0(2)(+))]O-16(0(6)(+)) when reconstructing the Hoyle state from three alpha particles. Therefore, no experimental signatures for alpha condensation were observed.
Experimental investigation of α condensation in light nuclei / Bishop, J.; Kokalova, T.; Freer, M.; Acosta, L.; Assie, M.; Bailey, S.; Cardella, G.; Curtis, N.; De Filippo, E.; Dell'Aquila, D.; De Luca, S.; Francalanza, L.; Gnoffo, B.; Lanzalone, G.; Lombardo, I.; Martorana, N. S.; Norella, S.; Pagano, A.; Pagano, E. V.; Papa, M.; Pirrone, S.; Politi, G.; Rizzo, F.; Russotto, P.; Quattrocchi, L.; Smith, R.; Stefan, I.; Trifiro, A.; Trimarchi, M.; Verde, G.; Vigilante, M.; Wheldon, C.. - In: PHYSICAL REVIEW C. - ISSN 2469-9985. - 100:3 (Article number 034320)(2019), pp. 1-20. [10.1103/PhysRevC.100.034320]
Experimental investigation of α condensation in light nuclei
Dell'Aquila D.;
2019-01-01
Abstract
Background: Near-threshold alpha-clustered states in light nuclei have been postulated to have a structure consisting of a diffuse gas of alpha 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 alpha condensation in light nuclei experimentally.Method: To examine signatures of this alpha condensation, a compound nucleus reaction using 160-, 280-, and 400-(MeVO)-O- 16 beams impinging on a carbon target was used to investigate the C-12(O-16, 7 alpha) reaction. This permits a search for near-threshold states in the alpha-conjugate nuclei up to Mg-24.Results: Events up to an alpha-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 7 alpha final states could be reconstructed to form Be-8 and( 12)C(0(2)(+)) showed a quantitative difference in which decay modes were dominant compared to the Fermi breakup model. No new states were observed in O-16, Ne-20, and Mg-24 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 multiparticle 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 O-16 was observed from [Si-28 *, C-12(0(2)(+))]O-16(0(6)(+)) when reconstructing the Hoyle state from three alpha particles. Therefore, no experimental signatures for alpha condensation were observed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
