1. DSM/DAPNIA, CEA Saclay, F-91191 Gif sur Yvette Cedex, France
2. Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
3. Centre de Recherches du Cyclotron, Université Catholique de Louvain, Chemin du cyclotron 2, B-1348 Louvain-la-Neuve, Belgium
4. GANIL, BP 55027, F-14076 Caen Cedex 5, France
5. Institut de Recherches Subatomiques, IN2P3-CNRS, F-67037 Strasbourg, Cedex 2, France
6. INFN, Laboratori Nazionali del Sud, Via Santa Sofia 44, 95123 Catania, Italy
7. Instituto de Fisica, Universidade de São Paulo, CP 66318, 05389-970, São Paulo, Brazil
8. University of Napoli and INFN Sezione di Napoli, I-80125, Napoli, Italy
9. Department of Nuclear Reactions, The Andrzej Soltan Institute for Nuclear Studies, Hoza 69, PL-00-681 Warsaw, Poland
10. Present address: DAM/DPTA/ Service de Physique Nucléaire, CEA DIF, F-91680 Bruyères-le-Châtel, France

Correspondence to: R. Raabe^1,2 Email: riccardo.raabe@fys.kuleuven.ac.be

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 freedom^{1, 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.

1. DSM/DAPNIA, CEA Saclay, F-91191 Gif sur Yvette Cedex, France
2. Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
3. Centre de Recherches du Cyclotron, Université Catholique de Louvain, Chemin du cyclotron 2, B-1348 Louvain-la-Neuve, Belgium
4. GANIL, BP 55027, F-14076 Caen Cedex 5, France
5. Institut de Recherches Subatomiques, IN2P3-CNRS, F-67037 Strasbourg, Cedex 2, France
6. INFN, Laboratori Nazionali del Sud, Via Santa Sofia 44, 95123 Catania, Italy
7. Instituto de Fisica, Universidade de São Paulo, CP 66318, 05389-970, São Paulo, Brazil
8. University of Napoli and INFN Sezione di Napoli, I-80125, Napoli, Italy
9. Department of Nuclear Reactions, The Andrzej Soltan Institute for Nuclear Studies, Hoza 69, PL-00-681 Warsaw, Poland
10. Present address: DAM/DPTA/ Service de Physique Nucléaire, CEA DIF, F-91680 Bruyères-le-Châtel, France

Correspondence to: R. Raabe^1,2 Email: riccardo.raabe@fys.kuleuven.ac.be

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