Abstract
Quantum tunnelling through a potential barrier (such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom1,2. A strong increase of the fusion probability has been observed for heavy deformed nuclei3. In light exotic nuclei such as 6He, 11Li and 11Be (termed ‘halo’ nuclei4), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial—it could induce a large enhancement of fusion5, but alternatively the weak binding energy of the nuclei could inhibit the process6. Other reaction channels known as direct processes (usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus 6He with a 238U target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the (large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.
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References
Caldeira, A. O. & Leggett, A. J. Influence of dissipation on quantum tunnelling in macroscopic systems. Phys. Rev. Lett. 46, 211–214 (1981)
Tsukada, M., Kobayashi, S. I., Kurihara, S. & Nomura, S. (eds) Proc. 4th Int. Symp. Foundations of Quantum Mechanics, Tokyo 1992 (Jpn. J. Appl. Phys. Ser. 9, The Institute of Pure and Applied Physics, Tokyo, 1993)
Stokstad, R. G. et al. Effect of nuclear deformation on heavy-ion fusion. Phys. Rev. Lett. 41, 465–469 (1978)
Austin, S. M. & Bertsch, G. F. Halo nuclei. Sci. Am. 272, 62–67 (1995)
Dasso, C. H. & Vitturi, A. Does the presence of 11Li breakup channels reduce the cross section for fusion processes? Phys. Rev. C 50, R12–R14 (1994)
Hussein, M. S., Pato, M. P., Canto, L. F. & Donangelo, R. Near-barrier fusion of 11Li with heavy spherical and deformed targets. Phys. Rev. C 46, 377–379 (1992)
Tanihata, I. et al. Measurements of interaction cross sections and nuclear radii in the light p-shell region. Phys. Rev. Lett. 55, 2676–2679 (1985)
Hansen, P. G. & Jonson, B. The neutron halo of extremely neutron-rich nuclei. Europhys. Lett. 4, 409–414 (1987)
Zhukov, M. V. et al. Bound state properties of Borromean halo nuclei: 6He and 11Li. Phys. Rep. 231, 151–199 (1993)
Beckerman, M. Sub-barrier fusion of two nuclei. Rep. Prog. Phys. 51, 1047–1103 (1988)
Dasso, C. H., Landowne, S. & Winther, A. Channel-coupling effects in heavy-ion fusion reactions. Nucl. Phys. A. 405, 381–396 (1983)
Rhoades-Brown, M. J. & Braun-Munziger, P. Explanation of sub-barrier fusion enhancement in a coupled channels model. Phys. Lett. B 136, 19–23 (1983)
Dasso, C. H., Guisado, J. L., Lenzi, S. M. & Vitturi, A. Coulomb- and nuclear-induced break-up of halo nuclei at bombarding energies around the Coulomb barrier. Nucl. Phys. A. 597, 473–486 (1996)
Hagino, K., Vitturi, A., Dasso, C. H. & Lenzi, S. M. Role of breakup processes in fusion enhancement of drip-line nuclei at energies below the Coulomb barrier. Phys. Rev. C 61, 037602 (2000)
Takigawa, N., Kuratani, M. & Sagawa, H. Effect of breakup reactions on the fusion of a halo nucleus. Phys. Rev. C 47, R2470–R2473 (1993)
Takahashi, J. et al. Is fusion inhibited for weakly bound nuclei? Phys. Rev. Lett. 78, 30–33 (1997)
Canto, L. F., Donangelo, R., de Matos, L. M., Hussein, M. S. & Lotti, P. Complete and incomplete fusion in heavy ion collisions. Phys. Rev. C 58, 1107–1117 (1998)
Dasgupta, M. et al. Fusion versus breakup: observation of large fusion suppression for 9Be + 208Pb. Phys. Rev. Lett. 82, 1395–1398 (1999)
Hinde, D. J. et al. Fusion suppression and sub-barrier breakup of weakly bound nuclei. Phys. Rev. Lett. 89, 272701 (2002)
Kolata, J. J. et al. Sub-barrier fusion of 6He with 209Bi. Phys. Rev. Lett. 81, 4580–4583 (1998)
Aguilera, E. F. et al. Transfer and/or breakup modes in the 6He + 209Bi reaction near the Coulomb barrier. Phys. Rev. Lett. 84, 5058–5061 (2000)
Trotta, M. et al. Large enhancement of the sub-barrier fusion probability for a halo nucleus. Phys. Rev. Lett. 84, 2342–2345 (2000)
Vandenbosch, R. & Huizenga, J. R. Nuclear Fission 463 (Academic, New York, 1973)
Ryckewaert, G., Colson, J. M., Gaelens, M., Loiselet, M. & Postiau, N. Recent results from the Louvain-la-Neuve RIB-facility. Nucl. Phys. A. 701, 323c–326c (2002)
Di Pietro, A. et al. Reactions induced by the halo nucleus 6He at energies around the Coulomb barrier. Phys. Rev. C 67, 044613 (2004)
Tamura, T. Compact reformulation of distorted-wave and coupled-channel Born approximations for transfer reactions between nuclei. Phys. Rep. 14, 59–96 (1974)
Thompson, I. J. Coupled reaction channels calculations in nuclear physics. Comput. Phys. Rep. 7, 167–212 (1988)
Kamimura, M. et al. Coupled-channels theory of breakup processes in nuclear reactions. Prog. Theor. Phys. Suppl. 89, 1–211 (1986)
Rusek, K., Keeley, N., Kemper, K. W. & Raabe, R. Dipole polarizability of 6He and its effect on elastic scattering. Phys. Rev. C 67, 041604 (2003)
Acknowledgements
R.R. is a Postdoctoral Researcher for the Fonds voor Wetenschappelijk Onderzoek - Vlaanderen. This work has been supported in part by the European Commission Fifth Framework programme on Access to Research Infrastructure.
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Raabe, R., Sida, J., Charvet, J. et al. No enhancement of fusion probability by the neutron halo of 6He. Nature 431, 823–826 (2004). https://doi.org/10.1038/nature02984
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DOI: https://doi.org/10.1038/nature02984
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