The structure of the nuclei begins with the so-called lower-order nuclei, as the deuterium H-2, tritium H-3 and helium He-3, which evolve into helium nucleus He-4 and then first upper-order oxygen nucleus O-16 that has four helium nuclei He-4 in a column of strong negative electric field. Furthermore, the second upper-order calcium nucleus Ca is based on the fundamental natural phenomenon of mirror symmetry, by repeating the first upper-order oxygen nucleus and its half, i.e. at the 2,5 factor. The same stands with the third upper-order tin nucleus Sn, which emerged from the second upper-order calcium nucleus Ca, according to the mirror symmetry and the same 2,5 factor. It is noted that the tin nucleus Sn will further form the basis for the structure of all heavy nuclei up to the radioactive uranium nucleus U-235. That is the simple and elegant structure model, according to which the nuclei consist of fixed helium nuclei He-4 (plus deuterium, tritium and helium He-3, all evolving into helium He-4) and neutrons rotating around of them.