Kotlyar V. Electromagnetic processes involving three–particle systems

The dissertation is devoted to development of methods in the theory of electromagnetic interaction with three–particle systems and to investigation of the 3He breakup by photons and electrons, as well as the radiative capture of protons by deuterons. Methods have been developed to study the influence of two–particle meson exchange currents on differential cross sections and polarization observables with numerical solutions of the Faddeev equations for the 3N bound state and taking into account the interaction in the continuous spectrum. The multipole decompositions of the nuclear–current Fourier transform are consistently constructed within the proposed approach. The proposed methods are used to analyze the mechanisms of radiative capture of protons by deuterons at energies below the pi–meson production threshold. The study of the meson exchange current influence on the observables in the radiative capture of protons by deuterons at energies below the pi–meson production threshold is supplemented by the research into the mechanisms of the two-body photodisintgration of 3He near and above this threshold. The final state of the reaction is described by the antisymmetrized product of the deuteron and proton wave functions. The calculations are carried out with the tensor wave function of the bound state of three nucleons. The inclusion of meson exchange currents significantly reduces the differences between the results of calculations and measurements. The meson exchange currents qualitatively change the character of the cross section and the photon analyzing power energy and angular distributions, which are obtained with S–waves. A model of meson exchange currents, which includes in the theory of photo–processes on atomic nuclei the off–the–energy–shell effects when real photons are absorbed by a system of interacting nucleons that belong to the mass shell, is developed. Account of these effects results in significant decrease in the meson exchange currents influence on the differential cross section of the reaction. A detailed analysis of the momentum distributions of nucleon and proton–deuteron clusters in oriented 3N nuclei is carried out using the tensor wave function of the bound state of three nucleons.