Study Of ? Decay Half-lives Within A Two-potential Approach

Alpha decay is a common and important decay mode, especially for heavy and super-heavy nuclei. We have obtained many useful properties of nuclear structure from the researches of alpha decay, such as the mass of atomic nucleus, the nuclear spin and parity, the radius and shape of nucleus, the nuclear shell structure, the energy levels of excited states, and so on. Some new isotopes, especially the neutron rich nucleus and super-heavy nucleus, are identified by measuring the particular alpha particles emitted by the nucleus belonging to the alpha decay line. Due to the similar decay mechanism, the theoretical models for alpha decay can be generalized to the study of the proton/two protons emission, the cluster emission and spontaneous fission.The two-potential approach is proposed to resolve the tunneling process of alpha decay by two separate parts: the problem of bound state due to the nuclear potential in the inner region and of scattering state in the outer region. The normalized factor, obtained by integration in the inner region, expresses the assault frequency. Based on WKB approximation, the penetration probability has been obtained. The mechanism of alpha particle preformation is related to the nuclear shell structure. We have analyzedthe experimental data of alpha decay half-lives from the latest nuclear properties table NUBASE2012, to obtain the alpha particle preformation factor. The coshgeometry potential is adopted as the nuclear potential designed to fit the experimental data.Based on the two-potential approach, this work includes the following three topics:(1) We used the cluster model to calculate the alpha decay half-lives of Europium isotopes. It is found that the numerical results agree well with the experimental data, and parameters of the nuclear potential linearly depend on isospin effect of nuclear.(2) We used the two-potential approach to systematically calculate the alpha decay half-lives of even-even nuclei, analyzing the isospin effect of the nuclear potential, adopting the isospin-dependent nuclear potential to slightly improve calculating precision of alpha decay half-lives, obtaining the parameters of phenomenological formula for alpha particle preformation hindrance factors through the experimental data of alpha decay half-lives. The calculated results can reproduce the experimental data for most of nuclei with a factor of two.(3) The alpha decay half-lives of nuclear isomers and corresponding ground states have been researched. We extracted the alpha particle preformation factor from the experimental data of alpha decay half-lives, analyzing the ratios of alpha particle preformation probabilities of nuclear isomers to those of corresponding ground states. It is found that nuclear isomers play no significant role on alpha decay. But some nuclear isomers of odd mass nuclei below the closed shell can be considered as an even-even nuclei plus a single nucleon at excited state, which have no effect on alpha particle preformation. In these nuclear isomers, the alpha particle preformation probabilities are greater than those of ground states. And the calculated results show that the ratios of alpha particle preformation probabilities in most of even-even nuclei and of nuclei where the sequence of energy levels cross are less than 1.At last, a summary of this work and some outlooks are given.