Nuclear magic numbers: New features far from stability

Abstract

a b s t r a c tThe main purpose of the present manuscript is to review the structural evolution along the isotonic and isotopic chains around the ''traditional '' magic numbers 8, 20, 28, 50, 82 and 126. The exotic regions of the chart of nuclides have been explored during the last three decades. Then the postulate of permanent magic numbers was definitely abandoned and the reason for these structural mutations has been in turn searched for. General trends in the evolution of shell closures are discussed using complementary experimental information, such as the binding energies of the orbits bounding the shell gaps, the trends of the first collective states of the even-even semi-magic nuclei, and the behavior of certain single-nucleon states. Each section is devoted to a particular magic number. It describes the underlying physics of the shell evolution which is not yet fully understood and indicates future experimental and theoretical challenges. The nuclear mean field embodies various facets of the nucleon-nucleon interaction, among which the spin-orbit and tensor terms play decisive roles in the shell evolutions. The present review intends to provide experimental constraints to be used for the refinement of theoretical models aiming at a good description of the existing atomic nuclei and at more accurate predictions of hitherto unreachable systems.

Shell evolution aboveZ,N=50within Skyrme density functional theory: The impact of deformation and tensor interactions

“…30 in Ref. [3]). Specifically, the 7/2 + 1 states for heavier isotones (Z > 44) and 1/2 + 1 states for lighter isotones (Z < 38) are considered to be mostly of s.p.…”

“…In particular, the observed trend of the shell evolution (SE) for states above Z, N =50 [3,5] can be consistently explained by including, in the effective shell model [6], a specific tensor contribution. This triggered a number of theoretical mean-field [7][8][9][10][11][12][13][14][15][16] and beyond mean-field studies [17][18][19][20].…”

“…This is similar to the case of 11/2 − states [42], where the experimental data were well explained in the context of shape-coexistence/shape-evolution employing a WoodsSaxon mean-field with the odd valence proton diabatically blocked when changing the β 2 deformation parameter. In addition, similarities of excitation energy curves between 11/2 − states in Sb isotopes and that of 3 − octupole collective states in neighboring Sn isotopes indicate considerable mixing, in Sb isotopes, between quasiparticle 11/2 − states and 3 − ⊗ 2d 5/2 particle-couplevibrational states [3].…”

“…With recent advances in the experimental techniques [3,4], it has been seen that neutron-rich nuclei with extremely large N/Z ratios can have shell structures which are considerably different from their respective stable isotopes or isotones. The shell variation (evolution) with nucleon number can be so drastic that one sees the disappearance of the conventional shell gaps (magic number) or the appearance of new ones in those exotic systems.…”

Properties of Intruder States in 34Al and 34Si

“…It has been shown in the last decades that the interaction between the valence protons and neutrons in neutron-rich nuclei can lead to a significant modification of the single particle energies resulting in the disappearance of the spherical magic numbers and the appearance of new ones [1]. It is in particular the case in the so called "island of inversion" centered around the N=20 32 Mg [2].…”