Electroexcitation of M2 giant resonances, mass dependent quenching of the spin-magnetism and the reduction of M1 strength in heavy nuclei

Knüpfer, W.; Frey, R.; Friebel, A.; Mettner, W.; Meuer, Daniel; Richter, A.; Spamer, E.; Titze, O.

doi:10.1016/0370-2693(78)90579-8

Cited by 91 publications

(11 citation statements)

References 14 publications

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“…For completeness, and in order to make some contact with measured 2-strength in (e,e-) reactions at low momentum transfer, we show in Fig. 6 the response to a ~ x q operator as in (18); the result is consistent with the concentration of strength observed at about 8 MeV [15]. This is unrelated to any collective pionic degrees of freedom and only subject to a quenching effect due to the repulsive g'.…”

Section: Excitation Functions At High Momentum Transfer For Unnaturalsupporting

confidence: 76%

“…The purpose of this investigation has been to obtain conceptual insight into the conditions under which pionic soft modes might develop in heavy, but finite nuclei. We have ignored many details and questions presently raised in connection with unnatural parity states in 2~ [15][16][17], e.g. about the mere location of M1 strength, which have to be answered before one might hope to embark on experimental studies at higher momentum transfers, e.g.…”

Section: Discussionmentioning

confidence: 98%

“…mode is obtained by multiplying its shell model expansion coefficients to either one of (15)(16)(17) and summing over all P-space basis states. The resultant forms, omitting the Yj*M (2), are denoted by Sj(a), Sj(~.q) and Sj(a x 2), respectively.…”

Section: (Ph;jmla~e~q"[o) ~Jl* ^-1 a Y* = ~ Q~h (Q)[ej (Q)]ll' Jl'mentioning

confidence: 99%

“…As examples, we shall choose J~=0-, 1 + and 2-states in 2~ the domain of interest being the excitation functions for these states at high momentum transfer. We note that the problem of magnetic excitations in 2~ has been a continuing challenge, both experimentally [15,16] and theoretically [17], even at low momentum transfer. Our aim here is not so much to improve on the low q situation, where the findings of Ref.…”

Section: Introductionmentioning

confidence: 99%

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The tensor force in heavy nuclei: High momentum collectivity of unnatural parity excitations

Toki

Weise

1980

Z Physik A

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The possibility of collectivity at high momentum transfer in unnatural parity states in finite nuclei, is outlined. This phenomenon is produced by the strong tensor force in the one pion exchange interaction operating coherently in a large oscillator space. The collectivity is observed at momenta q ~ (2-3) m~ corresponding to the critical momentum of pion condensation. If existent, such collective behaviour is expected to be seen in differential cross sections, e.g. for proton inelastic scattering, leading to unnatural parity states.

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Section: Excitation Functions At High Momentum Transfer For Unnaturalsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 98%

Section: (Ph;jmla~e~q"[o) ~Jl* ^-1 a Y* = ~ Q~h (Q)[ej (Q)]ll' Jl'mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The tensor force in heavy nuclei: High momentum collectivity of unnatural parity excitations

Toki

Weise

1980

Z Physik A

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“…1 Therefore, new theoretical concepts have been considered either to shift the isovector state to higher energies 6 or to quench the intrinsic g s factor in the Ml operator. 7 The experimental results reported in this Let-ter clarify the situation of the Ml strength in the bound-state region of 208 Pb. The 4.842-MeV state which has a ground-state radiative width of 5 eV [J5(Ml)t = 11.4/i 0 2 ] was originally classified as 1 + on the basis of a linear polarization measurement using a Compton polarimeter.…”

mentioning

confidence: 60%

Parity of Bound Dipole States inPb208

et al. 1982

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The parities of eleven J= 1 levels in 208 Pb were determined by nuclear resonance fluorescence scattering of linearly polarized photons. A new 1 + level at E x = 5.846 MeV with r 0 Vr= 1.2 ± 0.4 eV was found. This level can probably be identified with the theoretically predicted isoscalar 1 + state in 208 Pb. All other bound dipole states below 7 MeV with r 0 2 /r> 1.5 eV have negative parity. The 1" assignment to the 4.842-MeV level is of special significance because of previous conflicting results about its parity.PACS numbers: 21.10. Hw, 25.20.+y, 27.80.+w For more than a decade the location of magnetic dipole (Ml) strength in 208 Pb has been a challenging problem for experimentalists and theorists. 1 This continued interest lies in the fact that from the energies of the Ml excitations and their particle-hole structure one expects information about the spin-dependent part of the effective nucleon-nucleon interaction in nuclei. In a simple shell-model picture, two 1 + states are expected in 208 Pb resulting from the one-particle, one-hole (lp-lh) configurations v(i 13 / 2 ml 9 iu/2) and ir(h 11 / 2 " 1 9 h Q / 2 ). Since these states are nearly degenerate in energy they are expected to mix strongly and most of the strength is moved to higher energy. 2 In one calculation 3 the upper 1 + state at 7.5 MeV is mainly isovector and carries most of the strength [B(Ml)i = 48fi 0 2 ] while the lower 1 + state at 5.4 MeV is mainly isoscalar and has little strength [J3(Ml)* = 1.2/x 0 2 ]. The distribution of the Ml strength between these two states depends critically on the coupling between the neutron lp-lh and the proton lp-lh configurations. The inclusion of 2p-2h configurations 4 ' 5 results in the fragmentation of the upper state into many components. However, the properties of the lower level are virtually unchanged because of its very weak coupling to 2p-2h states. 4 ' 6 The present experimentally established Ml strength gives a completely different picture. Original claims, prior to 1977, of finding a large concentration of strengths [B(Ml)i>50(d 0 2 ] as expected in the 7.0-8.3-MeV region have been reduced to a total definitive and probable Ml strength above 7 MeV of only ^8.5ju 0 2 each. 1 Therefore, new theoretical concepts have been considered either to shift the isovector state to higher energies 6 or to quench the intrinsic g s factor in the Ml operator. 7 The experimental results reported in this Let-ter clarify the situation of the Ml strength in the bound-state region of 208 Pb. The 4.842-MeV state which has a ground-state radiative width of 5 eV [J5(Ml)t = 11.4/i 0 2 ] was originally classified as 1 + on the basis of a linear polarization measurement using a Compton polarimeter. 8 This result was afterwards questioned and a 1" assignment was established. 9 A repetition of the linear polarization measurement, 10 now with an enriched 208 Pb target, found an inconsistency with either a pure El or Ml transition and it was concluded that there are two levels (1 + and 1") at 4.842 MeV less than 3 keV apart ...

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Appendix Nuclear structure puzzles

Bertsch

Zamick

Mekjian

Nuclear Spectroscopy

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Electroexcitation of M2 giant resonances, mass dependent quenching of the spin-magnetism and the reduction of M1 strength in heavy nuclei

Cited by 91 publications

References 14 publications

The tensor force in heavy nuclei: High momentum collectivity of unnatural parity excitations

The tensor force in heavy nuclei: High momentum collectivity of unnatural parity excitations

Parity of Bound Dipole States inPb208

Appendix Nuclear structure puzzles

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