Atomic and Nuclear Physics

Biography

Biography: Xiaodong Li

Abstract

To explain some basic facts of atomic nucleus, a nuclear structure model of “ring plus extra nucleon” is proposed. For nuclei larger than ⁴He inclusive, protons (P’s) and neutrons (N’s) are basically bound alternatively to form a ^2Z_Z E ring. The ring folds with a “bond angle” of 90Ëš for every 3 continuous nucleons to make the nucleons packed densely. Extra N(‘s) can bind to ring-P with the same “bond angle” and “bond distance”. When 2 or more P’s are geometrically available, the extra N tends to be stable. Extra P can bind with ring N in a similar way when the ratio of N/P <1 although the binding is much weaker. Even-Z rings always have superimposed gravity centers of P and N; while for odd-Z rings, both centers of P and N must be eccentric. The eccentricity results in a depression of E_B and therefore specific zigzag features of E_B/A. This can be well explained by the shift of eccentricity by extra nucleons. Symmetrical center may present in even-Z rings and normal even-even nuclei. While for odd-Z ring, only anti-symmetric center (every P can find an N through the center and vice versa) is possible. Based on this model, a pair of mirror nuclei, P_X+nN_X and P_XN_X+n, should be equivalent in packing structure just like black-white photo and the negative film. Therefore, an identical spin and parity was confirmed for hundreds of pairs. In addition, the E_B/A difference of all the mirror nuclei pair is very nearly a constant of 0.184n MeV. Many other facts can also be easily understood from this model, such as the nuclear stabilities of isotopes in elements from He to Ne; the stability sequence of ⁹Be, ¹⁰Be, ⁷Be and ⁸Be; the neutron halo in neutron-rich nuclides; the general rule for most stable isotopes: odd-Z elements are odd A, even-Z elements are even A; and the highest cohesive energy of Li, Be, B atoms in their own elementary group and so on.