The structure of exotic nuclei around N = 28 is investigated in the sd-p f shell-model space usin... more The structure of exotic nuclei around N = 28 is investigated in the sd-p f shell-model space using a new effective interaction. The cross-shell part of the interaction is provided by the monopolebased universal interaction which has been successful in accounting for single-particle evolution in several mass regions. Focusing on the nuclear structure that is sensitive to the shell evolution, we show successful results for the proton-hole states in K isotopes and large deformation in 42 Si. The results demonstrate that the present scheme may be a promising way for constructing an effective interaction for other mass regions.
The evolution of the shell structure around N = 28 is described by the shell-model calculation us... more The evolution of the shell structure around N = 28 is described by the shell-model calculation using an effective interaction based on the monopole-based universal interaction. Performing shell-model calculations, we successfully describe the configuration mixing and deformation from which the shell evolution in this region is well clarified. The reduction of the proton spin-orbit splitting from N = 20 to 28 is dominated by the tensor force and is quantitatively reproduced well in terms of the distribution of the spectroscopic factors. This reduction also brings about a large oblate deformation in 42 Si. The location of the neutron 0g 9/2 orbit in Ca isotopes is identified by their 3 − 1 states.
Novel simple properties of the monopole component of the effective nucleon-nucleon interaction ar... more Novel simple properties of the monopole component of the effective nucleon-nucleon interaction are presented, leading to the so-called monopole-based universal interaction. Shell structures are shown to change as functions of N and Z consistently with experiments. Some key cases of this shell evolution are discussed, clarifying the effects of central and tensor forces. The validity of the present tensor force is examined in terms of the low-momentum interaction V lowk and the Q box formalism. PACS numbers: 21.30.Fe,21.60.Cs,21.10.-k,21.10.Pc
Single nucleon pickup reactions were performed with a 18:1 MeV=nucleon 14 O beam on a deuterium t... more Single nucleon pickup reactions were performed with a 18:1 MeV=nucleon 14 O beam on a deuterium target. Within the coupled reaction channel framework, the measured cross sections were compared to theoretical predictions and analyzed using both phenomenological and microscopic overlap functions. The missing strength due to correlations does not show significant dependence on the nucleon separation energy asymmetry over a wide range of 37 MeV, in contrast with nucleon removal data analyzed within the sudden-eikonal formalism.
We report no-core solutions for properties of light nuclei with three different approaches in ord... more We report no-core solutions for properties of light nuclei with three different approaches in order to assess the accuracy and convergence rates of each method. Full configuration interaction (FCI), Monte Carlo shell model (MCSM), and no core full configuration (NCFC) approaches are solved separately for the ground state energy and other properties of seven light nuclei using the realistic JISP16 nucleon-nucleon interaction. The results are consistent among the different approaches. The methods differ significantly in how the required computational resources scale with increasing particle number for a given accuracy.
... arising from the d3/2 orbital as the neutron number increases [6]. There may be several contr... more ... arising from the d3/2 orbital as the neutron number increases [6]. There may be several contributing factors causing such a signiï¬ cant drop in energy for the intruder alick.deacon@ manchester.ac.uk Current address: Argonne National Laboratory, Argonne, IL 60439, USA. ...
ABSTRACT The neutron-rich nucleus 30Na in the vicinity of the “Island of Inversion” was investiga... more ABSTRACT The neutron-rich nucleus 30Na in the vicinity of the “Island of Inversion” was investigated using intermediate-energy Coulomb excitation. A single γ-ray transition was observed and attributed to the 31+→2gs+ decay. A transition probability of B(E2;2gs+→31+)=147(21) e2 fm4 was determined and found in agreement with a previous experiment and with large-scale shell-model calculations. Evidence for the strong excitation of the 41+ state predicted by the shell-model calculations was not observed.
The shapes of neutron-rich exotic Ni isotopes are studied. Large-scale shell model calculations a... more The shapes of neutron-rich exotic Ni isotopes are studied. Large-scale shell model calculations are performed by advanced Monte Carlo Shell Model (MCSM) for the pf -g 9/2 -d 5/2 model space. Experimental energy levels are reproduced well by a single fixed Hamiltonian. Intrinsic shapes are analyzed for MCSM eigenstates. Intriguing interplays among spherical, oblate, prolate and γunstable shapes are seen, including shape fluctuations, E(5)-like situation, the magicity of doublymagic 56,68,78 Ni, and the coexistence of spherical and strongly deformed shapes. Regarding the last point, strong deformation and change of shell structure can take place simultaneously, being driven by the combination of the tensor force and changes of major configurations within the same nucleus.
The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is wel... more The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is well established. Recently developed large-scale shell-model calculations suggest a transitional region between normal-and intruder-dominated nuclear ground states, thus modifying the boundary of the island of inversion. In particular, a dramatic change in single-particle structure is predicted between the ground states of 30 Mg and 32 Mg, with the latter consisting nearly purely of 2p-2h N = 20 cross-shell configurations. Single-neutron knockout experiments on 30,32 Mg projectiles have been performed. We report on a first direct observation of intruder configurations in the ground states of these very neutron-rich nuclei. Spectroscopic factors to low-lying negative-parity states in the knockout residues are deduced and compare well with shell-model predictions.
The mechanism is studied which causes an anomalous magnetic moment of 9 C, i.e., too large isosca... more The mechanism is studied which causes an anomalous magnetic moment of 9 C, i.e., too large isoscalar spin for the Tz = ±3/2 mirror pair of A = 9, from a shell-model viewpoint. Based on the empirically determined shell energies varying from stable to unstable nuclei, the effective N = 8 shell gap for Z = 3 is evaluated to be rather narrow in a reasonable way. Under this condition, an additional shell quenching by the Thomas-Ehrman effect, arising for 9 C only, allows its ground state to be substantially mixed with the intruder configurations. This mirror asymmetry in the mirror wave functions accounts for the obviously large spin expectation value.
Spherical-deformed shape coexistence in the N ∼ 20 region is studied with the Monte Carlo shell m... more Spherical-deformed shape coexistence in the N ∼ 20 region is studied with the Monte Carlo shell model calculation. We focused upon the role of the configuration mixing in its description, and found that the deformed state is not correctly positioned until the mixing is treated in a proper way. It is also mentioned that the intruder component in 33 Al is accessible through the measurement of the magnetic moment.
Recent studies on exotic nuclei have rapidly advanced the understanding of the evolution of shell... more Recent studies on exotic nuclei have rapidly advanced the understanding of the evolution of shell structure, to which Takaharu Otsuka has made remarkable contributions particularly in terms of the nuclear force. This paper presents a brief survey of his achievements, focused on the concept of shell evolution due to the tensor force and the three-nucleon force and on related shell-model works.
The European Physical Journal A - Hadrons and Nuclei, 2004
Excited states in 136 Ba, populated in deep inelastic collisions by the interaction of 450 MeV 82... more Excited states in 136 Ba, populated in deep inelastic collisions by the interaction of 450 MeV 82 Se ions with a 139 La target, have been studied by means of in-beam γ-ray spectroscopy. A new isomer with I π = (10 + ) has been identified at an excitation energy Ex = 3.357 MeV. The half-life was determined as T 1/2 = 94 ± 10 ns. The extracted B(E2) value is much smaller than those in 132 Te and 134 Xe. This hindrance is investigated by a shell model calculation.
We discuss a mechanism of the anomalous spin expectation value of the 9 C-9 Li mirror pair in rel... more We discuss a mechanism of the anomalous spin expectation value of the 9 C-9 Li mirror pair in relation to the shell structure of exotic nuclei. In a similar way to the N = 20 shell gap for neutron-rich nuclei, the N = 8 shell gap should be rather narrow toward smaller Z from an empirical determination of the shell gap. The resulting ground state of 9 Li is still dominated by the normal configurations, whereas that of the mirror nucleus 9 C can be mixed with the intruder configurations triggered by the Thomas-Ehrman effect. This asymmetry of the ground state accounts for the experimental anomaly.
The structure of exotic nuclei around N = 28 is investigated in the sd-p f shell-model space usin... more The structure of exotic nuclei around N = 28 is investigated in the sd-p f shell-model space using a new effective interaction. The cross-shell part of the interaction is provided by the monopolebased universal interaction which has been successful in accounting for single-particle evolution in several mass regions. Focusing on the nuclear structure that is sensitive to the shell evolution, we show successful results for the proton-hole states in K isotopes and large deformation in 42 Si. The results demonstrate that the present scheme may be a promising way for constructing an effective interaction for other mass regions.
The evolution of the shell structure around N = 28 is described by the shell-model calculation us... more The evolution of the shell structure around N = 28 is described by the shell-model calculation using an effective interaction based on the monopole-based universal interaction. Performing shell-model calculations, we successfully describe the configuration mixing and deformation from which the shell evolution in this region is well clarified. The reduction of the proton spin-orbit splitting from N = 20 to 28 is dominated by the tensor force and is quantitatively reproduced well in terms of the distribution of the spectroscopic factors. This reduction also brings about a large oblate deformation in 42 Si. The location of the neutron 0g 9/2 orbit in Ca isotopes is identified by their 3 − 1 states.
Novel simple properties of the monopole component of the effective nucleon-nucleon interaction ar... more Novel simple properties of the monopole component of the effective nucleon-nucleon interaction are presented, leading to the so-called monopole-based universal interaction. Shell structures are shown to change as functions of N and Z consistently with experiments. Some key cases of this shell evolution are discussed, clarifying the effects of central and tensor forces. The validity of the present tensor force is examined in terms of the low-momentum interaction V lowk and the Q box formalism. PACS numbers: 21.30.Fe,21.60.Cs,21.10.-k,21.10.Pc
Single nucleon pickup reactions were performed with a 18:1 MeV=nucleon 14 O beam on a deuterium t... more Single nucleon pickup reactions were performed with a 18:1 MeV=nucleon 14 O beam on a deuterium target. Within the coupled reaction channel framework, the measured cross sections were compared to theoretical predictions and analyzed using both phenomenological and microscopic overlap functions. The missing strength due to correlations does not show significant dependence on the nucleon separation energy asymmetry over a wide range of 37 MeV, in contrast with nucleon removal data analyzed within the sudden-eikonal formalism.
We report no-core solutions for properties of light nuclei with three different approaches in ord... more We report no-core solutions for properties of light nuclei with three different approaches in order to assess the accuracy and convergence rates of each method. Full configuration interaction (FCI), Monte Carlo shell model (MCSM), and no core full configuration (NCFC) approaches are solved separately for the ground state energy and other properties of seven light nuclei using the realistic JISP16 nucleon-nucleon interaction. The results are consistent among the different approaches. The methods differ significantly in how the required computational resources scale with increasing particle number for a given accuracy.
... arising from the d3/2 orbital as the neutron number increases [6]. There may be several contr... more ... arising from the d3/2 orbital as the neutron number increases [6]. There may be several contributing factors causing such a signiï¬ cant drop in energy for the intruder alick.deacon@ manchester.ac.uk Current address: Argonne National Laboratory, Argonne, IL 60439, USA. ...
ABSTRACT The neutron-rich nucleus 30Na in the vicinity of the “Island of Inversion” was investiga... more ABSTRACT The neutron-rich nucleus 30Na in the vicinity of the “Island of Inversion” was investigated using intermediate-energy Coulomb excitation. A single γ-ray transition was observed and attributed to the 31+→2gs+ decay. A transition probability of B(E2;2gs+→31+)=147(21) e2 fm4 was determined and found in agreement with a previous experiment and with large-scale shell-model calculations. Evidence for the strong excitation of the 41+ state predicted by the shell-model calculations was not observed.
The shapes of neutron-rich exotic Ni isotopes are studied. Large-scale shell model calculations a... more The shapes of neutron-rich exotic Ni isotopes are studied. Large-scale shell model calculations are performed by advanced Monte Carlo Shell Model (MCSM) for the pf -g 9/2 -d 5/2 model space. Experimental energy levels are reproduced well by a single fixed Hamiltonian. Intrinsic shapes are analyzed for MCSM eigenstates. Intriguing interplays among spherical, oblate, prolate and γunstable shapes are seen, including shape fluctuations, E(5)-like situation, the magicity of doublymagic 56,68,78 Ni, and the coexistence of spherical and strongly deformed shapes. Regarding the last point, strong deformation and change of shell structure can take place simultaneously, being driven by the combination of the tensor force and changes of major configurations within the same nucleus.
The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is wel... more The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is well established. Recently developed large-scale shell-model calculations suggest a transitional region between normal-and intruder-dominated nuclear ground states, thus modifying the boundary of the island of inversion. In particular, a dramatic change in single-particle structure is predicted between the ground states of 30 Mg and 32 Mg, with the latter consisting nearly purely of 2p-2h N = 20 cross-shell configurations. Single-neutron knockout experiments on 30,32 Mg projectiles have been performed. We report on a first direct observation of intruder configurations in the ground states of these very neutron-rich nuclei. Spectroscopic factors to low-lying negative-parity states in the knockout residues are deduced and compare well with shell-model predictions.
The mechanism is studied which causes an anomalous magnetic moment of 9 C, i.e., too large isosca... more The mechanism is studied which causes an anomalous magnetic moment of 9 C, i.e., too large isoscalar spin for the Tz = ±3/2 mirror pair of A = 9, from a shell-model viewpoint. Based on the empirically determined shell energies varying from stable to unstable nuclei, the effective N = 8 shell gap for Z = 3 is evaluated to be rather narrow in a reasonable way. Under this condition, an additional shell quenching by the Thomas-Ehrman effect, arising for 9 C only, allows its ground state to be substantially mixed with the intruder configurations. This mirror asymmetry in the mirror wave functions accounts for the obviously large spin expectation value.
Spherical-deformed shape coexistence in the N ∼ 20 region is studied with the Monte Carlo shell m... more Spherical-deformed shape coexistence in the N ∼ 20 region is studied with the Monte Carlo shell model calculation. We focused upon the role of the configuration mixing in its description, and found that the deformed state is not correctly positioned until the mixing is treated in a proper way. It is also mentioned that the intruder component in 33 Al is accessible through the measurement of the magnetic moment.
Recent studies on exotic nuclei have rapidly advanced the understanding of the evolution of shell... more Recent studies on exotic nuclei have rapidly advanced the understanding of the evolution of shell structure, to which Takaharu Otsuka has made remarkable contributions particularly in terms of the nuclear force. This paper presents a brief survey of his achievements, focused on the concept of shell evolution due to the tensor force and the three-nucleon force and on related shell-model works.
The European Physical Journal A - Hadrons and Nuclei, 2004
Excited states in 136 Ba, populated in deep inelastic collisions by the interaction of 450 MeV 82... more Excited states in 136 Ba, populated in deep inelastic collisions by the interaction of 450 MeV 82 Se ions with a 139 La target, have been studied by means of in-beam γ-ray spectroscopy. A new isomer with I π = (10 + ) has been identified at an excitation energy Ex = 3.357 MeV. The half-life was determined as T 1/2 = 94 ± 10 ns. The extracted B(E2) value is much smaller than those in 132 Te and 134 Xe. This hindrance is investigated by a shell model calculation.
We discuss a mechanism of the anomalous spin expectation value of the 9 C-9 Li mirror pair in rel... more We discuss a mechanism of the anomalous spin expectation value of the 9 C-9 Li mirror pair in relation to the shell structure of exotic nuclei. In a similar way to the N = 20 shell gap for neutron-rich nuclei, the N = 8 shell gap should be rather narrow toward smaller Z from an empirical determination of the shell gap. The resulting ground state of 9 Li is still dominated by the normal configurations, whereas that of the mirror nucleus 9 C can be mixed with the intruder configurations triggered by the Thomas-Ehrman effect. This asymmetry of the ground state accounts for the experimental anomaly.
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Papers by Yutaka Utsuno