Experimental investigation of α condensation in light nuclei

J. Bishop; Tz Kokalova; M. Freer; L. Acosta; M. Assié; S. Bailey; G. Cardella; N. Curtis; E. De Filippo; D. Dell'Aquila; S. De Luca; L. Francalanza; B. Gnoffo; G. Lanzalone; I. Lombardo; N. S. Martorana; S. Norella; A. Pagano; E. V. Pagano; M. Papa; S. Pirrone; G. Politi; F. Rizzo; P. Russotto; L. Quattrocchi; R. Smith; I. Stefan; A. Trifirò; M. Trimarchì; G. Verde; M. Vigilante; C. Wheldon

doi:10.1103/PhysRevC.100.034320

Experimental investigation of α condensation in light nuclei

J. Bishop, Tz Kokalova, M. Freer, L. Acosta, M. Assié, S. Bailey, G. Cardella, N. Curtis, E. De Filippo, D. Dell'Aquila, S. De Luca, L. Francalanza, B. Gnoffo, G. Lanzalone, I. Lombardo, N. S. Martorana, S. Norella, A. Pagano, E. V. Pagano, M. PapaS. Pirrone, G. Politi, F. Rizzo, P. Russotto, L. Quattrocchi, R. Smith, I. Stefan, A. Trifirò, M. Trimarchì, G. Verde, M. Vigilante, C. Wheldon

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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
Article number	034320
Number of pages	20
Journal	Physical Review C
Volume	100
Issue number	3
DOIs	https://doi.org/10.1103/PhysRevC.100.034320
Publication status	Published - 20 Sept 2019

ASJC Scopus subject areas

Nuclear and High Energy Physics

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10.1103/PhysRevC.100.034320

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Bishop, J., Kokalova, T., Freer, M., Acosta, L., Assié, 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., ... Wheldon, C. (2019). Experimental investigation of α condensation in light nuclei. Physical Review C, 100(3), Article 034320. https://doi.org/10.1103/PhysRevC.100.034320

@article{c92fdfaeb8f1486aafa527fa5a40e6f6,

title = "Experimental investigation of α condensation in light nuclei",

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.",

author = "J. Bishop and Tz Kokalova and M. Freer and L. Acosta and M. Assi{\'e} and S. Bailey and G. Cardella and N. Curtis and {De Filippo}, E. and D. Dell'Aquila and {De Luca}, S. and L. Francalanza and B. Gnoffo and G. Lanzalone and I. Lombardo and Martorana, {N. S.} and S. Norella and A. Pagano and Pagano, {E. V.} and M. Papa and S. Pirrone and G. Politi and F. Rizzo and P. Russotto and L. Quattrocchi and R. Smith and I. Stefan and A. Trifir{\`o} and M. Trimarch{\`i} and G. Verde and M. Vigilante and C. Wheldon",

year = "2019",

month = sep,

day = "20",

doi = "10.1103/PhysRevC.100.034320",

language = "English",

volume = "100",

journal = "Physical Review C",

issn = "2469-9985",

publisher = "American Physical Society (APS)",

number = "3",

}

Bishop, J , Kokalova, T , Freer, M, Acosta, L, Assié, 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, NS, Norella, S, Pagano, A, Pagano, EV, Papa, M, Pirrone, S, Politi, G, Rizzo, F, Russotto, P, Quattrocchi, L, Smith, R, Stefan, I, Trifirò, A, Trimarchì, M, Verde, G, Vigilante, M & Wheldon, C 2019, 'Experimental investigation of α condensation in light nuclei', Physical Review C, vol. 100, no. 3, 034320. https://doi.org/10.1103/PhysRevC.100.034320

TY - JOUR

T1 - Experimental investigation of α condensation in light nuclei

AU - Bishop, J.

AU - Kokalova, Tz

AU - Freer, M.

AU - Acosta, L.

AU - Assié, M.

AU - Bailey, S.

AU - Cardella, G.

AU - Curtis, N.

AU - De Filippo, E.

AU - Dell'Aquila, D.

AU - De Luca, S.

AU - Francalanza, L.

AU - Gnoffo, B.

AU - Lanzalone, G.

AU - Lombardo, I.

AU - Martorana, N. S.

AU - Norella, S.

AU - Pagano, A.

AU - Pagano, E. V.

AU - Papa, M.

AU - Pirrone, S.

AU - Politi, G.

AU - Rizzo, F.

AU - Russotto, P.

AU - Quattrocchi, L.

AU - Smith, R.

AU - Stefan, I.

AU - Trifirò, A.

AU - Trimarchì, M.

AU - Verde, G.

AU - Vigilante, M.

AU - Wheldon, C.

PY - 2019/9/20

Y1 - 2019/9/20

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85072988391&partnerID=8YFLogxK

U2 - 10.1103/PhysRevC.100.034320

DO - 10.1103/PhysRevC.100.034320

M3 - Article

AN - SCOPUS:85072988391

SN - 2469-9985

VL - 100

JO - Physical Review C

JF - Physical Review C

IS - 3

M1 - 034320

ER -

Experimental investigation of α condensation in light nuclei

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