The monopole effect of the tensor force is presented, exhibiting how spherical single-particle energies are shifted as protons or neutrons occupy certain orbits. An analytic relation for such shifts is shown, and their general features are explained intuitively. Single-particle levels are shown to change in a systematic and robust way, by using the meson exchange tensor potential, consistently with the chiral perturbation idea. Several examples are compared with experiments. DOI: 10.1103/PhysRevLett.95.232502 PACS numbers: 21.60.ÿn, 21.10.ÿk, 21.30.Fe, 21.65.+f Shell structure characterizes finite quantum many-body systems. Atomic electrons confined by the Coulomb potential are subject to a well-known shell structure. For nuclei, since Mayer and Jensen [1], the shell structure has played a major role in clarifying nuclear structure. Recently, much progress has been made in the structure of exotic nuclei, which have rather extreme ratios of proton number (Z) to neutron number (N). Naturally, what new features can be found in their shell structure is of great and general interest.Along these lines, in this Letter, we present the variation of the nuclear shell structure due to the tensor force. The nucleon-nucleon (NN) interaction is originally due to meson exchange processes as predicted by Yukawa [2], and its tensor-force part is one of the most distinct manifestations of this meson exchange origin. As we shall show, the tensor force does indeed change the shell structure in a unique and robust way throughout the nuclear chart. The tensor force has been discussed over many decades. Its contribution to the spin-orbit splitting has been discussed, for instance, by Arima and Terasawa in terms of the second-order perturbation [3]. The importance of the tensor force for the nuclear binding energy has been demonstrated, for instance, by Pudliner et al. [4]. We shall show, in this Letter, how single-particle levels are changed systematically by the tensor force in the first order. The tensor force itself has certainly been included in various numerical calculations as one of the channels of the realistic nuclear force. Its first-order effect was discussed in individual cases, e.g., for 15 C and 16 O in [5]. In other early attempts, a possible tensor-force effect on the reduction of the spinorbit splitting was discussed in [6] with an example in the Os-Pb region [7]. The purpose of this Letter is, however, to present, for the first time, an analytic relation and a robust general feature, as well as concrete examples in close relation to experiments.The change of the shell structure, or the shell evolution, may have different origins. We focus upon the shell evolution due to the tensor force in this Letter. It is well known that the one-pion exchange process is the major origin of the tensor force, which is written aswhere~1 ;2 s 1;2 denotes the isospin (spin) of nucleons 1 and 2, K means the coupling of two operators in the brackets to an angular momentum (or rank) K, Y denotes the spherical harmonics for the Euler a...

The nuclear structure in regions of the Segré chart which are of astrophysical importance is reviewed. The main emphasis is put on those nuclei that are relevant for stellar nucleosynthesis in fusion processes, and in slow neutron capture, both located close to stability, rapid neutron capture close to the neutron dripline and rapid proton capture near the proton dripline. The basic features of modern nuclear structure, their importance and future potential for astrophysics and their level of predictibility are critically discussed. Recent experimental and theoretical results for shell evolution far off the stability line and consequences for weak interaction processes, proton and neutron capture are reviewed.

The 'Ni nucleus has been identified among the products of deep-inelastic reactions of Ni projectiles bombarding '3OTe and~o 'Pb targets. Three new states, including the high-lying 2+ (2033 keV) and the 0.86 ms 5 isomer, indicate a substantial subshell closure at neutron number N = 40. The level structure and the observed very slow E3 transition speed are discussed within the shell model. PACS numbers: 27.50.+e, 21.60.Cs, 23.20.Lv, 25.70.Lm In spherical nuclei the 1g9/2 orbital is distinctly separated in energy from all other single-particle levels. This gives rise to the well established magicity of the neutron and proton numbers N, Z = 50 and points towards a somewhat less pronounced closure at N, Z = 40. For protons the Z = 40 subshell closure is clearly demonstrated by the well known level structure of the 9OZr nucleus [1], for which the lowest excitation is the 1.76 MeV 0+ state, the first 2+ state appears at 2.19 MeV, and the lowest lying particle-hole (p,~2g9t2) excitation produces the longlived 5 isomeric state. The study of similar features in

New shell model Hamiltonians are derived for the T = 1 part of the residual interaction in the f 5/2 p 3/2 p 1/2 g 9/2 model space based on the analysis and fit of the available experimental data for 28 57 Ni 29 -28 78 Ni 50 isotopes and 29 77 Cu 50 -50 100 Sn 50 isotones. The fit procedure, properties of the determined effective interaction as well as new results for valence-mirror symmetry and seniority isomers for nuclei near 78 Ni and 100 Sn are discussed.Ni and 91 energy levels for [60][61][62][63][64][65][66][67][68][69][70][71][72] Ni. The nuclei below 60 Ni were not emphasized in the fit due to the increased role PHYSICAL REVIEW C 70, 044314 (2004)

The stability and spontaneous decay of naturally occurring atomic nuclei have been much studied ever since Becquerel discovered natural radioactivity in 1896. In 1960, proton-rich nuclei with an odd or an even atomic number Z were predicted to decay through one- and two-proton radioactivity, respectively. The experimental observation of one-proton radioactivity was first reported in 1982, and two-proton radioactivity has now also been detected by experimentally studying the decay properties of 45Fe (refs 3, 4) and 54Zn (ref. 5). Here we report proton-proton correlations observed during the radioactive decay of a spinning long-lived state of the lightest known isotope of silver, 94Ag, which is known to undergo one-proton decay. We infer from these correlations that the long-lived state must also decay through simultaneous two-proton emission, making 94Ag the first nucleus to exhibit one- as well as two-proton radioactivity. We attribute the two-proton emission behaviour and the unexpectedly large probability for this decay mechanism to a very large deformation of the parent nucleus into a prolate (cigar-like) shape, which facilitates emission of protons either from the same or from opposite ends of the 'cigar'.