Excitation energy and transition strength systematics of mixed symmetric Jπ = 1+ states from inelastic electron scattering

Hartmann, U.; Bohle, D.; Guhr, T.; Hummel, K.D.; Kilgus, G.; Milkau, Udo; Richter, A.

doi:10.1016/0375-9474(87)90297-1

Cited by 55 publications

(16 citation statements)

References 16 publications

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“…Sometimes more 1 + states are seen in (p,p') than in {e,e') and vice versa. A possible explanation is that some of the 1 + states correspond predominantly to the orbital (/) transitions, which are strongly excited by electrons but only weakly by protons (Bohle et aL, 1986;Hartmann et aL, 1987). In some cases a destructive interference between the orbital and spin parts of the Ml operator might occur in (e,e f ).…”

Section: Sp Sn T 3 (J)mentioning

confidence: 99%

Nuclear spin and isospin excitations

1992

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A review is given of our present knowledge of collective spin-isospin excitations in nuclei. Most of this knowledge comes from intermediate-energy charge-exchange reactions and from inelastic electron-and proton-scattering experiments. The nuclear-spin dynamics is governed by the spin-isospin-dependent two-nucleon interaction in the medium. This interaction gives rise to collective spin modes such as the giant Gamow-Teller resonances. An interesting phenomenon is that the measured total Gamow-Teller transition strength in the resonance region is much less than a model-independent sum rule predicts. Two physically different mechanisms have been discussed to explain this so-called quenching of the total Gamow-Teller strength: coupling to subnuclear degrees of freedom in the form of A-isobar excitation and ordinary nuclear configuration mixing. Both detailed nuclear structure calculations and extensive analyses of the scattering data suggest that the nuclear configuration mixing effect is the more important quenching mechanism, although subnuclear degrees of freedom cannot be ruled out. The quenching phenomenon occurs for nuclear-spin excitations at low excitation energies {co~ 10-20 MeV) and smallmomentum transfers {q < 0.5 fm~ *). A completely opposite effect is anticipated in the high (&>,#)-transfer region (0 < (o < 500 MeV, 0.5 < q < 3 fm~1). The nuclear spin-isospin response might be enhanced due to the attractive pion field inside the nucleus. Charge-exchange reactions at GeV incident energies have been used to study the quasifree peak region and the A-resonance region. An interesting result of these experiments is that the A excitation in the nucleus is shifted downwards in energy relative to the A excitation of the free proton. The physical origin of this shift is discussed, and it is shown that it may be related to the energy-dependent, attractive one-pion exchange interaction in the medium.

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Section: Sp Sn T 3 (J)mentioning

confidence: 99%

Nuclear spin and isospin excitations

1992

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“…The orbital mode 1 + states has been found for the isotopes with permanent deformation in a wide region beginning from light nuclei (such as 46 Ti) up to the actinides, including also transitional and γ-soft nuclei. [6][7][8][9][10][11][12][13] The remarkable features of the scissors mode obtained from experimental results are the quadratic dependence of the summed B(M1) values on the ground state deformation parameter δ and the strong fragmentation of the M1 strength above the pairing gap up to 4 MeV excitation energy. [14][15][16] There exists a strong correlation between the B(E2, 0 + 1 → 2 + 1 0) strength and summed B(M1) strengths and saturation of these strengths at midshell.…”

Section: Introductionmentioning

confidence: 99%

ROTATIONAL-INVARIANT MODEL OF THE STATES WITH K^π=1⁺ AND THEIR CONTRIBUTION TO THE SCISSORS MODE

Kuliev

Akkaya

Ilhan

et al. 2000

Int. J. Mod. Phys. E

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Within the Random-Phase Approximation the method of self-consistent determination of the isoscalar and isovector effective separable interactions restoring a broken symmetry of the deformed mean-field is given. The method allows to treat more rigorously without free parameters the properties of the scissors mode and is used to develop the rotational invariant microscopic model of the states with K π = 1 + . The spurious state separates out and has zero energy. An important consequence of this separation is the fragmentation of the scissors mode and the collectivization of the low-lying 1 + states. In addition to the isoscalar restoring interactions the consideration of the isovector restoring forces in calculations causes the splitting of the states with large B(M1) strength at low energy. The model contains a single parameter of isovector spin-spin interactions and it allows one to describe satisfactorily the fragmentation of the scissors mode and the dependence of the summed B(M1) strength on δ 2 and A in deformed nuclei.

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“…The latter approach breaks F -spin symmetry [9] and could cause a significant amount of F -spin mixing into the lowenergy states if the Majorana interaction were not too strong [10]. The properties of mixed-symmetry states with F -spin quantum number F = F max − 1 are very sensitive to the strength of the Majorana interaction [11] and, thus, to the amount of F -spin mixing in the lowenergy wave functions [12]. In fact, F -spin multiplets of states of neighboring nuclei, including Yb nuclei, have been observed for symmetric states with F = F max [11] and the scissors mode with F = F max − 1 [13].…”

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confidence: 99%

“…The properties of mixed-symmetry states with F -spin quantum number F = F max − 1 are very sensitive to the strength of the Majorana interaction [11] and, thus, to the amount of F -spin mixing in the lowenergy wave functions [12]. In fact, F -spin multiplets of states of neighboring nuclei, including Yb nuclei, have been observed for symmetric states with F = F max [11] and the scissors mode with F = F max − 1 [13]. These observations suggest that F -spin is not severely broken in the corresponding nuclei which may rule out an SU (3) ⋆ -like description even for the nuclei in the mass region A ≈ 170.…”

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confidence: 99%

Parity assignments inYb172,174using polarized photons and theKquantum number in rare earth nuclei

et al. 2005

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The 100 % polarized photon beam at the High Intensity γ-ray Source (HIγS) at Duke University has been used to determine the parity of six dipole excitations between 2.9 and 3.6 MeV in the deformed nuclei 172,174 Yb in photon scattering ( γ, γ ′ ) experiments. The measured parities are compared with previous assignments based on the K quantum number that had been assigned in Nuclear Resonance Fluorescence (NRF) experiments by using the Alaga rules. A systematic survey of the relation between γ-decay branching ratios and parity quantum numbers is given for the rare earth nuclei.PACS numbers: 21.10. Hw, 25.20.Dc, 27.70.+y Low-lying dipole excitations in heavy nuclei have been studied extensively using the Nuclear Resonance Fluorescence (NRF) or photon scattering method, which provides a model-independent way to determine excitation energies, spins, decay widths, decay branchings, and transition probabilities [1]. The parity of a nuclear state can be determined by either scattering unpolarized γ-rays and measuring polarization in the exit channel, or using linearly polarized γ-ray beam and measuring the azimuthal angular distribution of the scattered photons. For deformed even-even nuclei the K quantum number of J = 1 states can be assigned within the validity of the Alaga rules [2] from the electromagnetic decay branching ratio In general, there is no relation between the K quantum number and the parity of a J = 1 excitation [3]. However, restricting oneself to dipole excitations that carry the largest part of the excitation strength one selects collective modes for which certain selection rules may exist. Within realistic calculations for deformed nuclei in the framework of the interacting boson model (IBM) [4] with s-and d-proton and neutron bosons (sd-IBM-2), where negative parity states are not included, all J π = 1 + levels have a branching ratio corresponding to K = 1 (e.g. the bandheads of the K = 0 octupole vibrational band). This suggests that those states with J = 1 and branching ratios corresponding to K = 0 have negative parity. Positive parity has generally been assumed in previous works for all K = 1 excitations in the energy range of the M 1 scissors mode for calculating the summed B(M 1) strength, if no direct parity assignments were available. This rule of thumb was supported by γ-ray polarization measurements analyzing Compton-scattering asymmetries of the NRF γ-ray lines in some deformed nuclei of the Nd to Er even-even isotopic sequences [1]. It was concluded that at least the strong dipole excitations in sufficiently axially-symmetrically deformed nuclei decay according to the Alaga rules for ∆K = 1 (0) for positive (negative) parity.

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Excitation energy and transition strength systematics of mixed symmetric Jπ = 1+ states from inelastic electron scattering

Cited by 55 publications

References 16 publications

Nuclear spin and isospin excitations

Nuclear spin and isospin excitations

ROTATIONAL-INVARIANT MODEL OF THE STATES WITH K^π=1⁺ AND THEIR CONTRIBUTION TO THE SCISSORS MODE

Parity assignments inYb172,174using polarized photons and theKquantum number in rare earth nuclei

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Excitation energy and transition strength systematics of mixed symmetric Jπ = 1+ states from inelastic electron scattering

Cited by 55 publications

References 16 publications

Nuclear spin and isospin excitations

Nuclear spin and isospin excitations

ROTATIONAL-INVARIANT MODEL OF THE STATES WITH Kπ=1+ AND THEIR CONTRIBUTION TO THE SCISSORS MODE

Parity assignments inYb172,174using polarized photons and theKquantum number in rare earth nuclei

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ROTATIONAL-INVARIANT MODEL OF THE STATES WITH K^π=1⁺ AND THEIR CONTRIBUTION TO THE SCISSORS MODE