New magicity N = 32 and 34 due to strong couplings between Dirac inversion partners

Abstract

The novel nuclear structure in neutron-rich nuclei — the new magicity N=32 and 34 has been confirmed by the intensive experiment measurements (F. Wienholtz et al. (2013) [17]; D. Steppenbeck et al. (2013) [22]; S. Michimasa et al. (2018) [28]; etc.). However, the underlying mechanism of the new magicity is still under discussion. In this letter, we present a new mechanism that the strong couplings between the s1/2 (including both neutron and proton ones with different principle numbers) and neutron (ν) ν2p1/2 orbits, referred as “Dirac inversion partners” (DIPs) which are of the same total angular momentums but opposite parity, play a key role in opening both subshells at N=32 and 34. Such strong couplings originate from the inversion similarity between the DIPs, that the upper component of the Dirac spinor of one partner shares the same angular momentum as the lower component of the other, and vice versa. Following the revealed mechanism, it is predicted that on the proton deficient side (Z⩽20) the magicity N=32 is reserved from 52Ca until 48S, but vanishes in 46Si.