Non-capture breakup in the 6,7Li + 144Sm systems
D. Martinez Heimann 1*, A. Pacheco 1,2, A. Arazi 1,2, O. Capurro 1, M. Cardona 1,2, P. Carnelli 1,2, J. Fernández Niello 1,2, J. Figueira 1,2, D. Hojman 1,2, G. Martí 1, A. Negri 1,2
1 Laboratorio Tandar, Comisión Nacional de Energía Atómica,
Av. General Paz 1499, B1650KNA San Martín, Buenos Aires, Argentina
2 CONICET, Av. Rivadavia 1917, C1033AAJ Buenos Aires, Argentina
Breakup processes are one of the possible outcomes in nuclear reactions induced by either stable or unstable weakly bound projectiles. This may arise not only as a consequence of the elastic breakup of the projectile itself but also as the result of more complex processes that presumably involve the formation of a secondary weakly bound nucleus at some intermediate stage of the reaction. This is the case, for example, of neutron-stripping in 7Li-induced reactions followed by the breakup of the corresponding intermediate 6Li transfer product . Similar relatively involved mechanism have also been observed in reactions induced by other stable weakly bound projectiles such as 6Li  and 9Be . On the other hand in the last several years there has been intense debate regarding the role played by breakup reactions in determining the enhancement or hindrance of fusion cross sections . The issue has many facets. One of them relates to the general difficulties encountered in order to establish experimentally the occurrence of either one of those behaviors and the choice of an appropriate reference for comparison . The other aspect has to do with the availability of enough data from direct measurements of the so called non-capture breakup channel, especially at bombarding energies in the vicinity or below the Coulomb barrier. In this respect it is especially valuable to be able to obtain unambiguous data regarding, for instance, the non-capture character of the reaction and a complete experimental characterization of the asymptotic exit-channel configuration , as a prerequisite to any speculation on the dynamics in the short timescale relevant to the collision itself. In connection with the above discussion, we report in this contribution the results of the coincident detection of light particles emitted in reactions induced by 6Li and 7Li projectiles on the spherical 144Sm target at energies close or slightly below the Coulomb barrier. The experiments have been done using beams delivered by the 20UD tandem accelerator TANDAR in Buenos Aires. The emphasis of the measurements and of the analysis has been placed on the study of the correlations associated with the resonant and non-resonant breakup, from both elastic breakup and transfer/breakup reactions. We discuss several aspects related to the purely experimental determination of the main features that describe the reactions in terms of the distribution of the most relevant center-of-mass magnitudes such as the relative kinetic energies of the emitted light particles and the in-plane and out-of-plane angular distributions in the rest frame of the weakly bound nucleus that breaks up.
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