Electromagnetic response and breakup of light weakly bound nuclei in a dicluster model

Abstract

The light weakly-bound nucleus 7 Li is studied within a dicluster α + t picture. Different observables obtained within our simple model are compared with previous calculations and experiments showing good agreement. In particular we calculate dipole and quadrupole electromagnetic response to the continuum. The energy distribution of B(Eλ) values are consistent with the energy weighted molecular sum rule and display a sizable contribution of non-resonant character arising from the weak binding property. The corresponding form factors for excitations to the continuum are used in a semiclassical coupled channel scheme to get estimates for the break-up cross section in a heavy ion reaction. The nuclear contribution is found to play an important role in the process for bombarding energies around the Coulomb barrier. The masses and charges ratios of the two clusters are shown to lead to features of the cluster halo that may significantly differ from the one usually associated with one-nucleon haloes.

Strong reaction channels for the system17F +58Ni at Coulomb barrier energies

“…Finally, if we add up the contributions calculated for all direct processes, we get a cumulative cross section of (at least) 85-106 mb, which corresponds to 17-19% of the whole reaction cross section. This percentage is 50% larger than that for the benchmark reaction 16 O + 58 Ni [18], guiding to the conclusion that direct reaction channels are more strongly populated in the 17 F-induced reaction. This feature could be strongly related to the low binding energy of the 17 F valence proton.…”

“…Other stripping channels were not considered since they all involve the rather unfavorable breaking of the 16 O core in 17 F. Pick-up reactions were also disregarded following Q opt -arguments based on the semi-classical model of Brink [15]. Finally the breakup process was described according to a single-particle model [16,17], where the d 5/2 bound valence proton in 17 F, moving with respect to the 16 O core, is promoted to continuum states. Electric dipole (quadrupole) transitions to p 3/2 , f 5/2 and f 7/2 (s 1/2 , d 3/2 , d 5/2 , g 7/2 and g 9/2 ) continuum states were considered.…”

“…17 F is a rather exotic nucleus: it has a very low breakup threshold (S p = 0.600 MeV) and its first excited state at 0.4935 MeV has a well known proton-halo character [6]. The main aim of the experiment was to extract the reaction cross section and to compare it with that measured for the reaction induced by tightly-bound 16 O ions on a 58 Ni target in the same energy range.…”

Does the breakup process affect the reaction dynamics for the systems17O,17F +58Ni at Coulomb barrier energies?

“…Inelastic excitations leading to the first projectile and target excited states were included in the theoretical calculations with their experimental transition probabilities, the breakup process was described according to the single-particle model of Fortunato and Vitturi [11], while for transfer processes we followed the formalism of Brink [12]. The experimental data were fitted with the sum of the differential cross sections for all these direct channels.…”

“…An overall comparison of reactions induced by light loosely bound projectiles shows that the 11 Be [7], bound by S n = 0.504 MeV, exhibits by far the largest reactivity among all light projectiles. On the other side it should be very interesting to extend the measurements performed with the proton halo 8 B [8], bound only by S p = 0.1375 MeV, to the same energy range covered for the system 11 Be + 64 Zn.…”