Three-body forces and persistence of spin-orbit shell gaps in medium-mass nuclei: Toward the doubly magic ^{78}Ni (original) (raw)
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Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure
Bitlis Eren University Journal of Science and Technology
The interactions between the core which is anymore inert and the valence nucleons play a very important role in the interpretation of nuclear properties far from stability. The work done in this study is based on the calculations of energy spectra and electromagnetic properties for even-even isotones with N=52, in the 78 Ni region. Based on the interaction jj45apn with the space model jj45pn, we have realized some modifications considering the monopole interaction and a new interaction called jj45am is introduced. The calculations are performed in the framework of the nuclear shell model using the NuShellX@MSU code. The shell evolution, studied by estimating the effective single-particle energies (SPEs) in this region, show an important influence on the nuclear structure properties. The obtained results using the new interaction jj45am are in agreement with the experimental data, and better than those given by the original one jj45apn.
New subshell closure atN=58emerging in neutron-rich nuclei beyondNi78
Physical Review C, 2010
The structure of neutron-rich nuclei beyond 78 Ni was studied using postaccelerated radioactive beams of 83,84,85 Ga utilizing β γ and β-n γ spectroscopy. Our data, when combined with energy level systematics, suggests a possible new spherical subshell closure at N = 58 is created by the nearly degenerated ν3s 1/2 and ν2d 5/2 orbitals being well separated from other orbitals above N = 50. The near degeneracy of these states could be evidenced by isomerism in this region. The energies of the 2 + 1 and proposed 4 + 1 states observed in N = 52 84 Ge are interpreted as an indication of a possible weakening of the doubly magic 78 Ni core for nuclei beyond N = 50. The experimental evidence is supported by spherical HFB calculations using the SkO T functional involving the tensor term in the nucleon-nucleon interaction.
Nuclear structure far off stability --Implications for nuclear astrophysics
The European Physical Journal A, 2006
The single-particle structure and shell gap of 100 Sn as inferred from previous in-beam γ-ray spectroscopy has been confirmed in recent studies of seniority and spin-gap isomers by γγ, βγ, βpγ, pγ and 2pγ spectroscopy. The results for 94,95 Ag, 98 Cd and its N = 50 isotones 96 Pd and 94 Ru stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations, seniority mixing and E2 polarisation of the 100 Sn core. The strong monopole interaction of the ∆l = 0, 1 spin/isospin-flip partners πg 9/2 -νg 7/2 along the N = 50 isotones and the πf 5/2 -νg 9/2 pair of nucleons along the Z = 28 Ni isotopes are decisive for the evolution of the shell structure towards 100 Sn and 78 Ni. It can be traced back to the tensor force in the effective nucleon-nucleon interaction and provides a straightforward explanation for new shells in neutron-rich light nuclei, implying qualitative predictions for new N = 32, 34 subshells in Ca isotopes, persistence of the 78 Ni proton and neutron shell gaps and non-equivalence of the g 9/2 valence mirror Ni isotopes and N = 50 isotones. This is corroborated by recent experimental data on 56,58 Cr and 70-76 Ni. The implication of monopole driven shell evolution for apparent spin-orbit splitting towards N Z and structure along the astrophysical r-path between N = 50 and N = 82 is discussed.
Double magic nuclei for Z > 82 and N > 126
The "island of stability" of superheavy nuclei due to shell effects is explored and the α-decay half-lives of these nuclei are predicted. The calculations of the binding energies within a new macroscopic-microscopic model (MMM) are performed and compared with the experimental data for heavy nuclei from Md to the Z = 118 element. The agreement is excellent. The data confirm that the 270 Hs is a deformed double submagic nucleus beyond 208 Pb. The features of α-decay energies and one-proton-separation energies from the MMM reveal that the next double magic nucleus after 270 Hs should be 298 114. The potential energy surfaces calculated within the constrained relativistic mean-field (CRMF) theory show that the 270 Hs is a deformed double magic nucleus, but 298 114 is a spherical double magic nucleus. The α-decay half-lives are determined using a generalized liquid drop model (GLDM) with the Q α from the MMM for Hs and Z = 114 isotopes, respectively.
The half-life of the doubly-magic r-process nucleus 78Ni
The European Physical Journal A, 2005
Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutronrich nuclei play an important role in the astrophysical rapid neutron-capture process (r-process). 78 Ni is the only doubly-magic nucleus that is also an important waiting point in the r-process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of 78 Ni has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be 110 +100 −60 ms. In the same experiment, a first half-life was deduced for 77 Ni of 128 +27 −33 ms, and more precise half-lives were deduced for 75 Ni and 76 Ni of 344 +20 −24 ms and 238 +15 −18 ms respectively.
Study of the N=50 shell closure close to 78Ni
Brazilian Journal of Physics, 2004
The PARRNe (Production d'Atomes Radioactifs Riches en Neutrons) experimental program has been part of the recent R&D efforts for the design of the SPIRAL2 project at GANIL. The PARRNe2 setup installed at IPN-Orsay allows the use of the Tandem as a deuteron driver in order to produce mass separated fission fragment beams. The measured fission fragment yields proved to be high enough to undertake a series of β-decay experiments dedicated at studying the structure of proton-deficient nuclei close to N=50. We report here on two such experiments, the first being dedicated at the observation of the decay of 83 Ga→ 83 Ge (Z=32, N=51), 84 Ga→ 84 Ge (Z=32, N=52) and the second of the decay of 81 Zn→ 81 Ga (Z=31, N=50) allowing for the fist time the identification of a few γ lines with transitions in the daughter nuclei thus providing the material for a preliminary glimpse of their structure.
Study of the N = 50 major shell effect toward 78Ni at PARRNe⋆
The European Physical Journal A, 2006
The γ-ray de-excitations following the β-decay of 83 Ga and the β-n decay of 84 Ga have been studied. The radioactive species were produced using the PARRNe on-line mass-separator installed at the IPN Orsay Tandem accelerator. Two γ-lines were attributed to 83 Ge with the aid of β-γ and γ-γ coincidences. The Z identification of the γ-lines was provided by time analysis of a buid-up/decay cycle. The excited levels of 83 Ge can be explained by the coupling of the single neutron state ν2d 5/2 to the first 2 + excitation of the 82 Ge core. PACS. 29.30.-h Spectrometers and spectroscopic techniques-21.10.-k Properties of nuclei; nuclear energy levels-23.20.Lv gamma transitions and level energies-27.50.+e 59 ≤ A ≤ 89 Production d'Atomes Radioactifs Riches en Neutrons.
Physical Review C, 2004
The 70 Ni nucleus has been produced at the LISOL facility and its  decay to 70 Cu has been observed. In parallel, the 70 Cu nucleus has been produced at the ISOLDE facility. A new third -decaying isomeric state in 70 Cu has been identified, partly with the aid of the in-source laser spectroscopy method. Its measured half-life is T 1/2 =33͑2͒ s. In addition, two isomeric transitions in 70 Cu have been observed at energies of 101.1(3) and 141.3͑3͒ keV, and it allowed the relative placement of the three 70 Cu isomeric states and their tentative spin and parity assignments. The new 70 Cu isomer was found to be weakly populated in the  decay of 70 Ni. It allowed the construction of the 70 Ni decay scheme. Furthermore, the  decay of the three 70 Cu isomers to 70 Zn has been measured and their decay schemes are presented. The 70 Ni  decay to the isomeric states in 70 Cu and their subsequent isomeric decay and  decay to 70 Zn are discussed within the extreme shell-model picture of two valence nucleons outside the semidouble magic 28 68 Ni 40 core and it yields satisfactory results. Large-basis shell-model calculations using 28 56 Ni 28 as the core and a realistic effective interaction support rather well the suggested interpretation.