| 1. |
- Wilson, A. N., et al.
(författare)
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Magnetic dipole bands in 190Hg : First evidence of excitations across the Z = 82 sub-shell in Hg nuclei
- 2001
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 505:1-4, s. 6-14
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Tidskriftsartikel (refereegranskat)abstract
- An experiment aimed at studying high-spin states in 190Hg was performed with the Eurogam II array. The data have revealed the presence of cascades of magnetic dipole transitions with some unexpected properties. Unlike the MI bands previously observed in the heavier Hg isotopes, these structures have extremely large B(M1)/B(E2) ratios, The observation of a third dipole band with much lower B(M1)/B(E2) values in the same spin/excitation energy regime suggests that the bands may represent configurations occurring in different minima in the potential energy surface. Configuration-dependent Cranked Nilsson-Strutinsky calculations predict the presence of a minimum in the nuclear potential energy surface at a deformation of ε ≅ 0.2, γ ≅ -90°, occurring when a proton is excited across the Z = 82 shell-gap into an h9/2 orbital. It is suggested that the bands exhibiting anomalously large B(M1)/B(E2) ratios may be associated with this minimum.
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| 2. |
- Kelsall, N. S., et al.
(författare)
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Testing mean-field models near the N=Z line : gamma-ray spectroscopy of the T-z=1/2 nucleus Kr-73
- 2002
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 65:4
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Tidskriftsartikel (refereegranskat)abstract
- Excited states in the N=Z+1 nucleus Kr-73 have been investigated using the Ca-40(Ar-36,2pn) and Ca-40(Ca-40,alpha2pn) reactions at 145 and 160 MeV, respectively. gamma rays were detected using the Gammasphere array and events were recorded in coincidence with charged-particle and neutron detectors. The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring Kr-72,Kr-74, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may indicate the presence of T=0 pairing correlations. At high spin all the models can reproduce the experimental data.
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| 3. |
- Parry, C. M., et al.
(författare)
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First evidence for smooth band termination in valence space in the mass 130 region : Spectroscopy of 127La
- 2000
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 61:2, s. 213031-213035
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Tidskriftsartikel (refereegranskat)abstract
- High spin states in 127La have been studied using the 32S(100Mo,p4n) reaction at a beam energy of 155 MeV. Gamma rays were detected using the EUROBALL III spectrometer. One of the side bands in 127La is observed to be populated to a spin of 83/2+. These data are compared with cranked Nilsson-Strutinski calculations which suggest that the structure is a smoothly terminating band, in valence space, based upon a π[(g7/2d5/2)5(h11/2)2]⊗ ν[(g7/2d5/2)12(h11/2)6(d3/2s1/2)2] configuration, which can carry a maximum spin of 47.5ℏ. This is the first identification of such a structure in this mass region.
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| 4. |
- Pfohl, J., et al.
(författare)
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Highly deformed rotational structures in 136Pm
- 2000
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 62:3, s. 313041-313045
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Tidskriftsartikel (refereegranskat)abstract
- Four highly deformed structures in the odd-odd nucleus 13661Pm75 were observed via the 105Pd(35Cl,2p2n) reaction at 180 and 173 MeV using the GAMMASPHERE γ-ray spectrometer and the Microball charged-particle detector array. Quadrupole moment measurements were performed on all of the bands. In contrast to lighter odd-Ζ Pm and Pr nuclei, bands based on the g9/2[404]9/2 proton orbital were not observed. Instead, the four observed sequences are assigned as a coupling of an i13/2 neutron with the low-Ω h11/2 and mixed d5/2g7/2 orbitals. Comparisons with neighboring highly deformed structures are discussed and cranked Nilsson-Strutinsky calculations for 136Pm are presented.
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| 5. |
- Smith, J. F., et al.
(författare)
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Identification of excited states in 119Ba
- 2000
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 61:4
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Tidskriftsartikel (refereegranskat)abstract
- Excited states have been identified in the very neutron-deficient 119Ba nucleus. Two bands have been observed, which are likely to be based on h11/2 and (g7/2d5/2) neutron orbitals. Despite this being the first observation of excited states in 119Ba, the bands extend to (75/2)ℏ and (79/2)ℏ, respectively. The bands have been assigned to 119Ba using gamma-recoil and gamma-x-ray coincidences. Several quasiparticle alignments have been identified, involving neutron (h11/2)2 and proton (h11/2)2 aligned configurations. Furthermore, the bands show features which are reasonably consistent with smooth band termination at high spin. Theoretical results for 119Ba are discussed within the framework of cranked Woods-Saxon and Nilsson-Strutinsky calculations.
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| 6. |
- Wilson, A. N., et al.
(författare)
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High-spin structures and alignment properties in Ce-126
- 2001
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 6305:5
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Tidskriftsartikel (refereegranskat)abstract
- Excited states in Ce-126 have been observed with the GAMMASPHERE gamma -ray detector array, used in conjunction with the MICROBALL charged-particle detector. The reaction Zn-64(Zn-64, xpn alpha) (beam energy 260 MeV) was used to populate a wide range of nuclei in the neutron-deficient region with A approximate to 120. Ce-126 was populated via the 2p evaporation channel. The three previously observed bands have been extended to higher spins and some other structures have been identified. The yrast band shows evidence of a delayed neutron alignment occurring at a rotational frequency omega approximate to0.5 MeV/(h) over bar as observed in the neighboring odd-A nucleus Pr-127. One of the two excited bands shows evidence for a similar crossing at a slightly lower frequency and also exhibits a sudden gain in alignment at omega =0.57 MeV/(h) over bar. The third band may involve the coupling of a gamma -vibrational state. All three rotational bands are discussed in terms of standard and extended cranked shell model calculations.
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