Giant Magnetic Resonances

Raman, Subramanian; Fagg, L.W.; Hicks, Ross S.

doi:10.1142/9789814503495_0004

Cited by 16 publications

(11 citation statements)

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“…Summaries are provided e.g. by Berg and Kneissl (1987) and Raman et al (1991). The most exhaustive studies of M 1 strength distributions are available from (e, e ′ ) data covering all stable nuclides in the p-shell, N = Z and Z + 2 nuclides in the sd-shell, the stable Ca isotope chain, the N = 28 isotones, the open-shell nuclei 46,48 Ti, 50 Cr, 56 Fe, and finally 58 Ni.…”

Section: A Experimental Datamentioning

confidence: 99%

Magnetic dipole excitations in nuclei: Elementary modes of nucleonic motion

2010

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The nucleus is one of the most multi-faceted many-body systems in the universe. It exhibits a multitude of responses depending on the way one 'probes' it. With increasing technical advancements of beams at the various accelerators and of detection systems the nucleus has, over and over again, surprised us by expressing always new ways of 'organized' structures and layers of complexity. Nuclear magnetism is one of those fascinating faces of the atomic nucleus we discuss in the present review. We shall not just limit ourselves to presenting the by now very large data set that has been obtained in the last two decades using various probes, electromagnetic and hadronic alike and that presents ample evidence for a low-lying orbital scissors mode around 3 MeV, albeit fragmented over an energy interval of the order of 1.5 MeV, and higher-lying spin-flip strength in the energy region 5 − 9 MeV in deformed nuclei, nor to the presently discovered evidence for low-lying proton-neutron isovector quadrupole excitations in spherical nuclei. To the contrary, we put the experimental evidence in the perspectives of understanding the atomic nucleus and its various structures of well-organized modes of motion and thus enlarge our discussion to more general fermion and bosonic many-body systems.

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Section: A Experimental Datamentioning

confidence: 99%

Magnetic dipole excitations in nuclei: Elementary modes of nucleonic motion

2010

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“…This study, whose initial results were reported brielly in [27,28], is, to our knowledge, the first theoretical investigation of possible electric contributions to M1 cross sections of even-even nuclei, measured experimentally at a backward scattering angle. The topic is of some general interest, because the backward electron stattering has established itself since three decades as one of the main tools for the experimental study of nuclear magnetic dipole excitations due to its particular sensitivity towards the magnetic response at backward angles [1][2][3][4][5][6].…”

Section: Summary and Cocci Usiqnsmentioning

confidence: 99%

“…The momentum transfer has throughout this article the inverse dimension of length (fm '); i.e. , q/ft is denoted by q.The peculiar selectivity of the backward (e, e ') scattering towards magnetic excitations was used extensively in the last decades to study Ml transitions mainly in spherical nuclei [4,6]. The M 1 operator can excite there particle-hole states, which are spin-orbit partners.…”

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confidence: 99%

Competing electric and magnetic excitations in backward electron scattering from heavy deformed nuclei

1995

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Important E2 contributions to the (e, e ) cross sections of low-lying orbital Ml excitations are found in heavy deformed nuclei, arising from the small energy separation between the two excitations with I K= 2+1 and 1+1,respectively. They are studied microscopically in QRPA using DWBA. The accompanying E2 response is negligible at small momentum transfer q but contributes substantially to the cross sections measured at t/= 165' for 0.6(q,«(0.9 fm ' (40~E;~70 MeV) and leads to a very good agreement with experiment. The electric response is of longitudinal C2 type for (9~175 but becomes almost purely transverse E2 for larger backward angles. The transverse E2 response remains comparable with the M1 response for q, «) 1.2 fm ' (E;~100 MeV) and even dominant for E;)200 MeV. This happens even at large backward angles 0~175', where the M1 dominance is limited to the lower q region. PACS number(s): 25.30.Dh, 21.60.Jz, 27.70.+q I. MOTIVATION Inelastic electron scattering at a backward angle 0=180' was used by Peterson and co-workers [1,2] more than 30 years ago to study nuclear magnetic dipole (Ml) excitations at the linear accelerator in Stanford. The predominance of M 1 excitations in backward scattering is expected from qualitative considerations [2] of the (e,e ') cross section in the plane wave Born approximation (PWBA). The cross section can be decomposed in this case into longitudinal (Coulomb) and transverse (electric and magnetic) terms, multiplied by corresponding kinematical factors. The electric field of the incoming electron can have both longitudinal and transverse components, while its magnetic field is purely transverse. If the electron rest mass and the nuclear excitation energy can be neglected in comparison with the incident electron energy, which is often the case with low-lying excitations, the longitudinal kinematical factor vanishes for 0=180' and only transverse multipoles are excited by the inelastic scattering [3]. The (e, e ') cross section can be related further to the transition probability for photoabsorption through approximate considerations within the "virtual photon" method. One arrives in this way at the rough qualitative estimate [2] for dominant magnetic over electric transverse excitations (both of the same multipolarity). This property is due to the momentum transfer during electron scattering. It stands in contrast with the corresponding relationship for radiative excitation, where no momentum is transferred and the EL excitation is one order of magnitude stronger than the ML excitation (L stands for multipolarity). Electronic address: roland. noj arov uni-tuebingen. dẽ Electronic address: amand. faessler uni-tuebingen. dẽ Electronic address: michael. ding felder uni-tuebingen. de dominance at a backward angle can be drawn by assuming a purely spin-fiip transition [4]. The transverse electric field of the incoming electron is negligibly small in this particular case if the excitation energy E is small in comparison with the transferred momentum q, i.e. , E &&qfi, c. The same result...

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“…It is noteworthy that based on arguments similar to expanded above, in Refs. [36,37] it was shown that magnetic dipole resonance (MDR), experimentally detected by NRF technique as well [38], can also be interpreted as a result of perturbation-induced corelayer decomposition of nucleus, but accompanied by differentially rotational, torsional, elastic oscillations of peripheral layer relative to static core, as pictured in Fig.6. To this end, it worth emphasizing that macroscopic elastodynamic treatment of low-frequency dipole nuclear resonant excitations provides a remarkable way of unifying understanding of the electric pygmy dipole resonance and magnetic dipole resonance as soft modes of differentially translational (PDR) and differentially rotational (MDR) elastic oscillations of the finite-depth layer against static core, respectively, the oscillations driven by one and the same restoring force of shear deformations.…”

Section: Discussion and Summarymentioning

confidence: 95%

Elasticity of nuclear medium as a principal macrodynamical promoter of electric pygmy dipole resonance

Баструков¹,

Молодцова²,

Podgainy³

et al. 2008

Physics Letters B

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Motivated by arguments of the nuclear core-layer model formulated in [S.I. Bastrukov, J.A. Maruhn, Z.Phys. A 335 (1990) 139], the macroscopic excitation mechanism of the electric pygmy dipole resonance (PDR) is considered as owing its origin to perturbationinduced effective decomposition of a nucleus into two spherical domains -undisturbed inner region treated as a static core and dynamical layer undergoing elastic shear vibrations. The elastic restoring force is central to the excitation mechanism under consideration and has the same physical meaning as in macroscopic model of nuclear giant resonances involving distortions of the Fermi-sphere providing unified description of isoscalar giant electric and magnetic resonances of multipole degree ℓ ≥ 2 in terms of two fundamental vibrational modes in an elastic sphere, to wit, as spheroidal (electric) and torsional (magnetic) modes of shear elastic oscillations of the nodeless field of material displacements excited in the entire nucleus volume. In the present paper focus is placed on the emergence of dipole overtone in the frequency spectrum of spheroidal elastic vibrations as Goldstone soft mode. To emphasis this feature of dipole resonant excitation imprinted in the core-layer model we regain spectral equation for the frequency of spheroidal elastic vibrations trapped in the finite-depth layer, derived in the above paper, but using canonical equation of an elastic continuous medium. The obtained analytic equations for the frequency of dipole vibrational state in question and its excitation strength lead to the following estimates for the PDR energy centroid E P DR (E1) = [31 ± 1] A −1/3 MeV and the total excitation probability B P DR (E1) = [1.85 ± 0.05] 10 −3 Z 2 A −2/3 e 2 fm 2 throughout the nuclear chart exhibiting fundamental character of this soft dipole mode of nuclear resonant response. PACS: 21.60.Ev; 24.30.Cz.

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Giant Magnetic Resonances

Cited by 16 publications

References 1 publication

Magnetic dipole excitations in nuclei: Elementary modes of nucleonic motion

Magnetic dipole excitations in nuclei: Elementary modes of nucleonic motion

Competing electric and magnetic excitations in backward electron scattering from heavy deformed nuclei

Elasticity of nuclear medium as a principal macrodynamical promoter of electric pygmy dipole resonance

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