Exotic structure of halo nuclei has been stimulating many researchers in nuclear physics. The neutron halo, which is composed of either one or few weakly bound neutrons, has an extensive density distribution with a large tail. This is due to a vanishing binding energy of the last neutron at the drip line where the continuum states of neutrons should play an important role.Breakup reactions have been a useful probe for the structure of the halo nuclei. In fact, large reaction cross sections were observed in halo systems, which provided a proof for the large radius. Recently, precise measurements of the breakup cross section, such as angular distributions and excitation spectra at low energies, become possible. The novel information gives us an opportunity to study quantitatively the structure and excitation mechanism of the halo nuclei, which has motivated the present theoretical study.In order to make a quantitative analysis on the breakup reactions at low energies, one needs a reaction theory which can describe the quantum breakup reactions with high accuracy. Recently, we have exploited a method of calculating the quantum scattering [1], the absorbing boundary condition (ABC) method which is widely used in the quantum chemistry. In order to handle the complicated continuum states in the halo nuclei, we adopt the grid-point representation of wave functions and solve a differential equation in the coordinate space. This enables us to take into account all the coupling to the continuum in computing the scattered wave functions. A judicious choice of the ABC takes care of the complicated outgoing boundary condition for the scattered waves of breakup particles.
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