PHYSICAL REVIEW C 71, 027602 (2005) Fusion, reaction, and breakup cross sections of 9 Be on a light mass target G. V. Mart´ ı, 1 P. R. S. Gomes, 2 M. D. Rodr´ ıguez, 1,3 J. O. Fern´ andez Niello, 1,3 O. A. Capurro, 1 A. J. Pacheco, 1 J. E. Testoni, 1 M. Ram´ ırez, 1 A. Arazi, 1 I. Padron, 2 R. M. Anjos, 2 J. Lubian, 2 and E. Crema 4 1 Laboratorio Tandar, Departamento de F´ ısica, Comisi ´ on Nacional de Energ´ ıa At ´ omica, Av. del Libertador 8250, (1419), Buenos Aires, Argentina 2 Instituto de F´ ısica, Universidade Federal Fluminense, Av. Litorˆ anea, s/n, Gragot´ a, Niter ´ oi, R.J., 24210-340, Brazil 3 Escuela de Ciencia y Tecnolog´ ıa, Universidad de Gral, San Mart´ ın, Argentina 4 Departamento de F´ ısica Nuclear, Universidade de S˜ ao Paulo, Caixa Postal 66318, 05315-970, S˜ ao Paulo, S.P., Brazil (Received 8 November 2004; published 28 February 2005) The total fusion cross section for the 9 Be + 27 Al system has been measured at energies close and above the Coulomb barrier. Reaction cross sections for this system were derived from elastic scattering data, and the breakup-plus-transfer-channel cross sections were estimated from the difference between these data and measured cross-section fusion. DOI: 10.1103/PhysRevC.71.027602 PACS number(s): 25.60.Gc, 25.70.Jj, 25.70.Mn, 25.60.Dz The breakup (BU) process of weakly bound nuclei and its influence on the fusion cross section has become a subject of great recent interest. To study this subject, different processes following the breakup should be considered: elastic breakup (EBU), when neither of the breakup fragments is captured by the target (actually the term noncapture breakup should be more appropriate, because the breakup process involves a transfer of kinetic energy for the excitation into the continuum); incomplete fusion reaction (ICF), when one of the fragments is captured by the target; and complete fusion following BU (CF BU ), when all breakup fragments are captured by the target. Therefore, the total breakup cross section is the sum of three contributions: EBU, ICF, and CF BU , whereas the sum of complete fusion (including two body fusion and CF BU ) and incomplete fusion is called total fusion (TF). The most studied weakly bound nuclei are the stable 9 Be, 6 Li, and 7 Li that have threshold breakup energies for different processes between 1.48 and 2.55 MeV and the radioactive neutron rich halo nuclei 6 He, 11 Li, and 11 Be, whose threshold breakup energies are in the range 0.33–0.98 MeV. The breakup of all these nuclei is usually described as leading to two fragments. The Li isotopes produce two charged fragments ( 6 Li −→ α + d; 7 Li −→ α + t), whereas 9 Be and 11 Be break up into one neutron and 8 Be and 10 Be, respectively. In the breakup of 6 He −→ α + (2n) and 11 Li −→ 9 Li + (2n), the two neutrons are usually considered as a di-neutron fragment. However, the breakup of 9 Be is more complex than that, because the 8 Be is an unstable isotope and decays into two α particles, with a half-life of 0.7 fs. The 9 Be itself may undergo a prompt breakup process 9 Be −→ α + α + n (Q = −1.57 MeV) or 9 Be −→ α + 5 He (Q =−2.47 MeV). Therefore, the 9 Be breakup could be described as a process in which the excitation of the 9 Be to energies above the particle emission threshold for one or more decay channels, as a result of which it dissociates, ultimately leading to the production of α particles [1]. Hinde et al. [2] performed very impressive exclusive experiments on the subbarrier breakup of 9 Be on 208 Pb, and they were able to distinguish the prompt breakup from the long-lived 8 Be ground-state breakup following transfer or the Coulomb excitation of the target nucleus. Experimentally, it is very difficult to discriminate the usual two-body complete fusion from CF BU , and it is not easy to separate direct transfer reactions from ICF leading to the same final nucleus. In addition, the separation of the CF from the ICF is not an easy task. Usually the emitted evaporation residues following both groups of processes are very similar or identical, and therefore the direct identification of residues is not able to distinguish them. This similarity is even more evident for light systems for which the main evaporation channels include charged particles. This is the reason why most of the available data in the literature correspond to total fusion cross sections, although there are few reports of some measurements of CF and ICF separately. The measurement of EBU cross sections requires exclusive experiments of coincidence between charged particle fragments. A measurement of the total fusion cross section for systems with 9 Be includes the following processes: fusion of 9 Be with target, fusion of 8 Be with target, fusion of one neutron plus 8 Be with target, fusion of one neutron plus two α-particles with target, fusion of α particle with target, and α particle transferred to the target. In some experiments [3–5] with heavy targets, it was possible to separate the fusion of α particles from the fusion of 9 Be and 8 Be with the target. When experiments involve the measurement of single α particles, the yield of α particles corresponds to the following expression: σ α-singles = σ ICF + 2(σ transfer + σ EBU ) [1], (1) where σ ICF corresponds to one α fragment fusing with the target, σ transfer is the one-neutron transfer to the target, and the 8 Be breaking up into two α’s. The yield of two α particles in coincidence corresponds to the following: σ α-coincidences = σ transfer + σ EBU . (2) Hinde et al. [2] concluded that for the 9 Be + 208 Pb, the prompt breakup results largely from a process close to the nuclear surface (nuclear field) excitation and is the mechanism 0556-2813/2005/71(2)/027602(4)/$23.00 027602-1 ©2005 The American Physical Society