Studies of nuclear shell closures N=16, 20, 28, and 40

The main scientific activity that I have carried out since my thesis is centered on the study of N = 14; 16; 20, N = 28 and N = 40 nuclear layer closures for very neutron rich nuclei. In the first part of the manuscript, I have chosen to develop more particularly the research theme on the N = 28 nuclear layer closure. It is a subject that came up repeatedly during these years of research. I found it interesting to review it in a different way than the publications. The accomplished efforts are underlined, as well as the future perspectives both in nuclear structure and astrophysics. In the following parts, I summarize the other main research topics that I have tackled since my hiring at the CNRS in 1991, on N = 14; 16; 20 and N = 40 layer closures. I briefly mention the discoveries that seem important to me, and refer to the articles published on these subjects. For each of the mentioned regions, the means of investigation used to study these neutron rich nuclei are multiple and complementary. They also depend of course on the intensity of the produced nuclei. We have thus used spectroscopic methods of β decays, Coulombian excitation, γ de-excitation in flight of nuclei produced by fragmentation, and transfer reaction. I particularly emphasize the essential results and the (sometimes innovative) techniques used. (author)