Nuclear spin and isospin excitations

Journal Article · Wed Apr 01 00:00:00 EST 1992 · Reviews of Modern Physics; (United States)

DOI:https://doi.org/10.1103/RevModPhys.64.491· OSTI ID:7205987

Osterfeld, F ^[1]

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1. Institut fuer Kernphysik, Forschungszentrum Juelich GmbH, Postfach 1913, 5170 Juelich (Germany)

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 {Delta}-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 ({omega}{similar to}10--20 MeV) and small-momentum transfers ({ital q}{le}0.5 fm{sup {minus}1}). A completely opposite effect is anticipated in the high ({omega},{ital q})-transfer region (0{le}{omega}{le}500 MeV, 0.5{le}{ital q}{le}3 fm{sup {minus}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 {Delta}-resonance region. An interesting result of these experiments is that the {Delta} excitation in the nucleus is shifted downwards in energy relative to the {Delta} excitation of the free proton.

• OSTI ID: 7205987
• Journal Information: Reviews of Modern Physics; (United States), Vol. 64:2; ISSN 0034-6861
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
NUCLEAR STRUCTURE
COLLECTIVE EXCITATIONS
AXIAL-VECTOR CURRENTS
CHARGE-EXCHANGE INTERACTIONS
CURRENT ALGEBRA
DELTA-1232 BARYONS
DIRECT REACTIONS
DISTORTED WAVE THEORY
ELECTROMAGNETIC INTERACTIONS
G MATRIX
GAMOW-TELLER RULES
GIANT RESONANCE
INELASTIC SCATTERING
ISOSPIN
ISOVECTORS
MAGNETIC DIPOLES
MATRIX ELEMENTS
MOMENTUM TRANSFER
NUCLEAR REACTIONS
NUCLEON-NUCLEON INTERACTIONS
PIONS
PROTON-NEUTRON INTERACTIONS
QUASI-FREE REACTIONS
QUENCHING
RANDOM PHASE APPROXIMATION
RESONANCE SCATTERING
REVIEWS
SHELL MODELS
SPIN
SPIN FLIP
STRENGTH FUNCTIONS
STRONG INTERACTIONS
SUM RULES
WEAK INTERACTIONS
ALGEBRAIC CURRENTS
ANGULAR MOMENTUM
BARYON-BARYON INTERACTIONS
BARYONS
BASIC INTERACTIONS
BOSONS
CURRENTS
DELTA BARYONS
DIPOLES
DOCUMENT TYPES
ELEMENTARY PARTICLES
ENERGY-LEVEL TRANSITIONS
EQUATIONS
EXCITATION
FERMIONS
FUNCTIONS
HADRON-HADRON INTERACTIONS
HADRONS
INTERACTIONS
MATHEMATICAL MODELS
MATRICES
MESONS
MULTIPOLES
N BARYONS
NUCLEAR MODELS
PARTICLE INTERACTIONS
PARTICLE PROPERTIES
PROTON-NUCLEON INTERACTIONS
PSEUDOSCALAR MESONS
RESONANCE
SCATTERING
TENSORS
VECTORS
663110* - General & Average Properties of Nuclei & Nuclear Energy Levels- (1992-)