| 1. |
- Fujita, Y, et al.
(författare)
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Evidence for the existence of the [202]3/2 deformed band in mirror nuclei Mg-25 and Al-25
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 92:6
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Tidskriftsartikel (refereegranskat)abstract
- After 50 years of its prediction, the highest-lying [2 0 2]3/2 orbit among the six Nilsson single-particle orbits originating from the sd shells in prolately deformed nuclei and the rotational band on this orbit were identified. The band members were observed in Al-25 at excitation energies of 6-7.5 MeV in a high-resolution Mg-25(He-3,t) charge-exchange reaction at 0degrees having a strong selectivity for Gamow-Teller transitions. In the comparison with the analogous M1 transitions in Mg-25, the J(pi)=3/2(+) bandhead state and the excited 5/2(+) and 7/2(+) members were clearly assigned.
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| 2. |
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| 3. |
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| 4. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Dominance of low-l component in weakly bound deformed single-neutron orbits
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 69:4
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Tidskriftsartikel (refereegranskat)abstract
- Calculating single-particle (Nilsson) levels in axially symmetric quadrupole-deformed potentials in coordinate space, the structure of weakly bound neutron orbits is studied in the absence of pair correlation. It is shown that in the wave functions of Omega(pi)=1/2(+) orbits, where Omega expresses the projection of the particle angular momentum along the symmetry axis, the l=0 (s(1/2)) component becomes overwhelmingly dominant as the binding energy of the orbits approaches zero, irrespective of the size of the deformation and the kind of Nilsson orbits. Consequently, all Omega(pi)=1/2(+) levels become practically unavailable for both deformation and many-body pair correlation, when the levels approach continuum or lie in the continuum.
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| 5. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Isoscalar dipole strength in Pb-208(82)126: The spurious mode and the strength in the continuum
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:4
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Tidskriftsartikel (refereegranskat)abstract
- The isoscalar dipole (compression) mode is studied first using the schematic harmonic-oscillator model, and then the self-consistent Hartree-Fock (HF) and random-phase approximation (RPA) are solved in coordinate space. Taking Pb-208 and the SkyM* interaction as a numerical example, the spurious component and the strength in the continuum are carefully examined using the sum rules. It is pointed out that in the continuum calculation one has to use an extremely fine radial mesh in HF and RPA in order to separate, with good accuracy, the spurious component from intrinsic excitations.
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| 6. |
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| 7. |
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| 8. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Pair correlation in neutron drip line nuclei
- 2003
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 68:3: 034312
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Tidskriftsartikel (refereegranskat)abstract
- The Hartree-Fock-Bogoliubov (HFB) equation in a simplified model is solved in coordinate space with the correct asymptotic boundary conditions, in order to study the pair correlation in nuclei close to the neutron drip line. The occupation probability obtained in the HFB approach for lower-l orbits decreases considerably already when the binding energy of the corresponding Hartree-Fock (HF) one-particle level becomes smaller. When the HF one-particle level enters into the continuum, the lower-l orbit soon becomes almost unavailable for the pair correlation of the many-body system. In contrast, the contribution to the pair correlation by high-l orbits which have one-particle resonant levels with narrow width in the HF potential can be estimated in the BCS approximation using the one-particle resonant energies, though the associated wave functions in the HFB approach are bound-state wave functions.
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| 9. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Polarization charge of particles near threshold due to the coupling to shape oscillations
- 2002
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Ingår i: Proceedings of the International Symposium on Nuclear Electro-Weak Spectroscopy for Symmetries in Electro-Weak Nuclear-Processes. in Honor of Professor Hiro Ejiri. - 9812381252 ; , s. 261-266
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Konferensbidrag (refereegranskat)abstract
- It is shown that the isoscalar strength in the energy region just above the low energy threshold, which is created by exciting particles to the continuum in nuclei far from β-stability lines, can be reduced by the attractive coupling to isoscalar shape oscillations. This is in contrast to the well known fact that in β-stable nuclei low lying isoscalar particle hole strengths are always increased by the attractive isoscalar coupling, which leads to an appreciable amount of positive polarization charge. On the other hand, the core polarization effect on bound particles with l=0 and 1 is always positive, but vanishes as the binding energy approaches to zero
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| 10. |
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| 11. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Quantized wobbling excitations with alignments
- 2003
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 67:1: 014319
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Tidskriftsartikel (refereegranskat)abstract
- The wobbling excitations in the presence of an appreciable amount of alignment are expected to appear more easily at lower angular momenta of the yrast spectra, compared with those in the textbook example. The large B(E2;I-->I-1) value for Delta(n) over cap =1 transitions where (n) over cap expresses the number of wobbling phonons is shown to be a strongly increasing function of the triaxiality parameter gamma, especially for gammagreater than or similar to+20degrees, while it is relatively independent of moments of inertia. On the other hand, the relation of the wobbling phonon energy to the total angular momentum may be used to extract quantitative information on nuclear moments of inertia. It is concluded that the gamma value of the triaxial, strongly deformed bands in Lu-163 is about equal to +20degrees and may be slightly increasing as a function of I.
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| 12. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Quantized Wobbling in Nuclei
- 2003
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Ingår i: Nuclear Physics News. ; 13:No.3, s. 20-20
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Tidskriftsartikel (refereegranskat)
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| 13. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Shape, shell structure and collective modes unique to nuclei far from stability line
- 2002
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Ingår i: Progress of Theoretical Physics Supplement. - 0375-9687. ; :146, s. 143-152
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Konferensbidrag (refereegranskat)abstract
- The structure of nuclei far from beta-stability lines is expected to show various interesting and exotic phenomena, due to the unique features: (a) the presence of nucleons with very small binding energies and largely extended wave-functions; (b) large difference between the Fermi levels of protons and neutrons; (c) exotic ratios of the proton to neutron numbers for a given mass number. Among the topics, which are the direct consequence of those characteristic features and are being studied experimentally using the radioactive nuclear ion beam facilities in the world, I choose to talk about the one-particle shell-structure, response function, and related collective modes.
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| 14. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Shell-structure and pair-correlation in nuclei close to the neutron drip line
- 2004
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Ingår i: Nuclear Physics, Section A. - : Elsevier BV. - 0375-9474. ; 731, s. 211-223
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Tidskriftsartikel (refereegranskat)abstract
- First, in the absence of pair correlation the properties of one-particle orbits of neutrons in nuclei close to the neutron drip line are briefly reviewed for both weakly bound neutrons and the neutrons in the continuum. The low-lying states in the continuum, which are close to the Fermi level, are of immediate importance for pair correlation and deformations of those nuclei. Then, the Hartree-Fock-Bogoliubov (HFB) equation in a simplified model is solved in coordinate space with the correct asymptotic boundary conditions, in order to provide quantitative characterization of both the role of weakly bound neutrons and the effect of the resonances in the continuum on pairing correlations.
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| 15. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Two-phonon states in nuclei - From surface vibrations to wobbling motion
- 2003
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Ingår i: Frontiers of Collective Motions (CM2002). - : WORLD SCIENTIFIC. - 9789812381989 ; , s. 376-386
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Konferensbidrag (refereegranskat)abstract
- Being stimulated by the recent identification of the two-phonon wobbling excitation, first I make a brief survey of various two-phonon states in nuclear physics, in connection with experimental observations. Then, I discuss the wobbling-phonon excitation in the presence of particle alignments, which is nicely pinned down in the recent experiments of the nucleus Lu-163(71)92.
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| 16. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Weakly-bound p3/2 neutrons and spin-response function in the many-body pair-correlation of neutron drip line nuclei
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 70:3
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Tidskriftsartikel (refereegranskat)abstract
- Solving the simplified model of the Hartree-Fock Bogoliubov equation in coordinate space with the correct asymptotic boundary conditions, the spin-orbit splitting, occupation probabilities, effective pair-gap, mean square radius, and spin-response function are studied for weakly bound p neutrons. As the binding energy of p3∕2 neutrons becomes small or approaches zero, the spin-orbit splitting p3∕2−p1∕2 in the one-body potential drastically decreases and, at the same time, the effective pair-gap for the p neutrons becomes small, while the occupation probability of the p3∕2 level decreases only slightly. Consequently, in that limit low-lying broader spin response with almost constant amount of total strength appears with the peak moving toward very low excitation energies.
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| 17. |
- Hamamoto-Kuroda, Ikuko, et al.
(författare)
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Weakly bound s(1/2) neutrons in the many-body pair correlation of neutron drip line nuclei
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 69:6
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Tidskriftsartikel (refereegranskat)abstract
- With a simplified model in the Hartree-Fock-Bogoliubov (HFB) approximation, the behavior of weakly bound s(1/2) neutrons in the many-body pair correlation is studied by solving the HFB equation in coordinate space with the correct asymptotic boundary conditions. It is shown that in one-neutron pickup reactions on the even-even neutron-drip-line nuclei, which contain loosely bound s(1/2) neutrons, the strength of the s(1/2) neutron can appear both at a discrete state and in the low-energy continuum spectra, with comparable strength. When there is no weakly bound discrete state, the continuum spectra may exhibit a sharp peak just above E-x=lambda, which originates from the resonantlike behavior of the upper component of the HFB radial wave function, u(s1/2)(E-qp,r). This resonantlike behavior may be directly observed as an s-wave resonance close to E-x=/lambda in neutron-scattering experiments on those nuclei. It is also shown that a very large root-mean-square radius of loosely bound s(1/2) neutrons may appear also in the presence of many-body pair correlation, since the effective pair gap in weakly bound neutron orbits with low l values is much reduced.
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| 18. |
- Hamamoto-Kuroda, Ikuko
(författare)
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Wobbling excitations in odd-A nuclei with high-j aligned particles
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 65:4
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Tidskriftsartikel (refereegranskat)abstract
- Using the particle-rotor model in which one high-j quasiparticle is coupled to the core of triaxial shape, wobbling excitations are studied. The family of wobbling phonon excitations can be characterized by: (a) very similar intrinsic structure while collective rotation shows the wobbling feature; (b) strong B(E2;I-->I-1) values for Deltan(w)=1 transitions where n(w) expresses the number of wobbling phonons. For the Fermi level lying below the high-j shell with the most favorable triaxiality gammaapproximate to+20degrees, the wobbling phonon excitations may be more easily identified close to the yrast line, compared with the Fermi level lying around the middle of the shell with gammaapproximate to-30degrees. The spectroscopic study of the yrast states for the triaxial shape with -60degrees<γ<0 are illustrated by taking a representative example with gamma=-30degrees, in which a quantum number related with the special symmetry is introduced to help the physics understanding.
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| 19. |
- Jensen, DR, et al.
(författare)
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Coexisting wobbling and quasiparticle excitations in the triaxial potential well of Lu-163
- 2004
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 19:2, s. 173-185
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states of the nucleus Lu-163 have been populated through the fusion-evaporation reaction La-139(Si-29, 5n) with a beam energy of 157 MeV. In addition to the two lowest excited triaxial strongly deformed (TSD) bands, recently interpreted as one- and two-phonon wobbling excitations, a third excited TSD band has been firmly established decaying to the yrast TSD band. The assignment of this band as a three-quasiparticle band shows together with the normal deformed (ND) level scheme the presence not only of shape coexistence between ND and TSD structures, but also an interplay of wobbling and quasiparticle excitations in the triaxial strongly deformed potential well of Lu-163.
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| 20. |
- Jensen, DR, et al.
(författare)
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Evidence for second-phonon nuclear wobbling
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89:14
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Tidskriftsartikel (refereegranskat)abstract
- The nucleus Lu-163 has been populated through the reaction La-139(Si-29,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2)(out)/B(E2)(in) value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation.
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| 21. |
- Jensen, DR, et al.
(författare)
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Wobbling phonon excitations, coexisting with normal deformed structures in Lu-163
- 2002
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Ingår i: Nuclear Physics, Section A. - 0375-9474. ; 703:1-2, s. 3-44
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Tidskriftsartikel (refereegranskat)abstract
- Wobbling is a rotational mode unique to a triaxial body. The Lu-Hf isotopes with N similar to 94 at high spin provide a possible region of nuclei with pronounced triaxiality. We have investigated Lu-163 through the fusion-evaporation reaction La-139(Si-29,5n)Lu-163 with a beam energy of 152 MeV. Three excited bands decaying into the known, presumably triaxial, superdeformed (TSD) band built on the i(13/2) proton orbital are observed. The electromagnetic properties of the connecting transitions from the two strongest populated excited TSD bands have been investigated. New particle-rotor calculations in which one i(13/2) quasiproton is coupled to the core of triaxial shape produce a variety of bands, whose properties can clearly be interpreted either as "wobbling" or "cranking" motion of the core. Evidence for the assignment of the excited TSD bands as one, and possibly even two wobbling phonon modes built on the yrast TSD band in Lu-163 is given. These triaxial bands coexist with bands built on quasiparticle excitations in the normal deformed (ND) minimum for which new data are also presented.
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| 22. |
- Koike, T, et al.
(författare)
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Chiral bands, dynamical spontaneous symmetry breaking, and the selection rule for electromagnetic transitions in the chiral geometry
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:17
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Tidskriftsartikel (refereegranskat)abstract
- A model for a special configuration in triaxial odd-odd nuclei is constructed which exhibits degenerate chiral bands with a sizable rotation, a manifestation of dynamical spontaneous symmetry breaking. A quantum number obtained from the invariance of the model Hamiltonian, which characterizes observable states, is given and selection rules for electromagnetic transition probabilities in chiral bands is derived in terms of this quantum number. The degeneracy of the lowest two bands is indeed obtained in the numerical diagonalization of the Hamiltonian at an intermediate spin range, over which electromagnetic transitions follow exactly the selection rule expected for the chiral geometry.
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| 23. |
- Shimbara, Y, et al.
(författare)
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Suppression of Gamow-Teller and M1 transitions in deformed mirror nuclei Mg-25 and Al-25 - Direct observation of K selection rules
- 2004
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 19:1, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- The mirror nuclei Mg-25 and Al-25 are expected to have very similar structures. The Gamow-Teller (GT) transitions from the J(pi) = 5/2(+) ground state of Mg-25 to the excited states in Al-25 were studied by high-resolution measurements of the Mg-25(He-3,t) charge-exchange reaction at 0degrees and at 140 MeV/nucleon. Assuming the usual DeltaJ(pi) = 1(+) selection rule for the spin-isospin-type GT transitions, the states with J(pi) = 3/2(+), 5/2(+), and 7/2 (+) should be excited. However, of the more than ten states with these J(pi) values below 6 MeV excitation energy, only the 5/2 (+) ground state and the 7/2 (+) , 1.613 MeV state in Al-25 were strongly populated, while all other states were strongly suppressed. The analysis of M1 transitions in Mg-25 also suggested a very similar feature for the analogous M1 transitions. Both Mg-25 and Al-25 are known to be largely deformed, and most low-lying states can be interpreted in terms of one-particle quantum numbers in the deformed potential and the associated rotational spectra. The observed suppression can be explained in terms of the K quantum number selection rules that are inherent to axially deformed nuclei.
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