Study of electromagnetic reactions on light nuclei with the Lorentz Integral Transform method

In this thesis, which is conducted in the field of few-body nuclear physics, we apply the recently developed method of the Lorentz Integral Transform (LIT) to the study of inelastic electromagnetic reactions on light nuclei. The two basic electromagnetic reactions, i.e. nuclear photoabsorption and electron scattering off nuclei, are treated. The LIT enables one to perform exact calculations, avoiding the complication of the explicit evaluation of the continuum final states and reducing the problem to the solution of a bound state like equation. With this method the final state interaction is fully taken into account. The bound state like calculations are performed with an hyperspherical harmonics expansion, whose convergence is accelerated by building an effective interaction in the hyperspherical formalism (EIHH). In this work we present the first microscopic calculation of the total photoabsorption cross sections below pion production of 6Li, 6He and 7Li. The calculations are performed with simple central semirealistic NN-interactions, which simulate partially the tensor force, since they reproduce binding energies of two and three-body nuclei. The obtained photoabsorption cross section of 6Li shows a single broad giant dipole resonance, while the one of 6He presents two well separated peaks corresponding to the break up of the neutron halo and the alpha-core, respectively. The comparison with experimental data shows that the addition of a P-wave interaction improves substantially the agreement with data. For 7Li a single broad giant dipole resonance is found and a good agreement with the available experimental data is achieved. As concerns the electron scattering reaction, we present a calculation of the longitudinal and transverse response functions for 4He in the quasi-elastic region at medium momentum transfers. A non-relativistic model for the electromagnetic charge and current excitation operators is used. The calculation is performed with a semirealistic interaction and a gauge invariant model is build by construction of a meson exchange current. The effect of the two-body current on the transverse response is investigated and preliminary results are discussed. The comparison of the first results with the available experimental data is also shown