Structura fina in dezintegrare alfa

Mihail Mirea
DFT Seminar Room
2020-03-05 12:00:00


A new system of microscopic equations of motion was recently deduced by starting from the variational principle. It is a generalization of the well-known time-dependent pairing equations for the case of odd-nucleons systems, and are obtained by including two mixing configurations mechanisms: the Landau-Zener effect and the Coriolis coupling. These equations provide information about the dissipated energy, the distributions of intrinsic and collective angular momenta, and the probabilities of different seniority-1 configurations, by following the rearrangement in time of the nuclear orbitals during the disintegration process, starting from the initial compound nucleus and reaching the scission. As an application, these equations are solved in order to investigate the fine structure of the alpha-decay of an odd-A mass nucleus, as the simplest modality to test the theory. The alpha-decay is treated as a superasymmetric fission process. In usual theories concerning the disintegrations, the alpha particle is always preformed on the nuclear surface, the dynamics of its formation being unclear. However, even if one considers that the alpha particle preexists in the parent nucleus, it cannot appear suddenly on the surface of the daughter. As stated many years ago, due to the extreme saturation of nuclear matter, the states of the nucleons mainly depend on the boundaries of the many-body potential. If the alpha particle preexists in the parent nucleus and it is moving to the external region, implicitly the nuclear shape of the whole system is modified. That is, all the nucleons states are perturbed during the alpha-decay process. Therefore, a picture consisting of an overlap between an unperturbed initial state and a final configuration should be not sufficient to take into account the whole complexity of the process. In this contribution, the alpha-decay of the 211Po and 211Bi parent nuclei was studied by modifying the boundaries of the many-body potential, in the same manner as realized in the case of fission-like theories. A superasimmetric fission path was obtained by using the least action principle in the framework of the macroscopic-microscopic model. The level scheme is calculated within the Woods-Saxon two center shell model. The probabilities of finding the excited states of the daughter at scission are obtained from the microscopic equations of motion. These probabilities have the same meaning as the spectroscopic ones. The intensities of the transitions to the excited states of the daughter were evaluated theoretically. The experimental data were compared with the theoretical findings. A very good agreement was obtained. A mean value of the tunneling velocity of about 2 × 10^4 fm/fs was extracted.

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