Isospin symmetry-breaking in compound and precompound nuclear reactions. [unified model]

Journal Article · Tue Sep 06 04:00:00 EDT 1977 · Ann. Phys. (N.Y.); (United States)

DOI:https://doi.org/10.1016/0003-4916(77)90211-1· OSTI ID:5460585

Feinstein, R L

The preequilibrium formalism of the Unified Theory of Nuclear Reactions serves as the formal framework for studying the consequence of isospin symmetry-breaking. A T-violating generalization of the energy-average fluctuation cross section is obtained by (a) choosing a ''chained-partition'' representation of the closed-channel Hilbert space, from the ''simple'' doorway through subspaces of increasing ''complexity,'' (b) introducing explicitly the symmetry-breaking component of the A-body Hamiltonian, (c) following its effects through the entire formal framework, and (d) applying standard statistical approximations. An isospin-conversion mechanism emerges in an explicit microscopic representation. Its functional relationship to the mean isospin-mixing interaction strength is realized by performing an approximate diagonalization of a realistic subspace and by employing random matrix theory. Our analysis suggest that near ''complete'' mixing is common in compound as well as some precompound processes and that its energy dependence can be very rapid. Simplifications of the general formula are noted. One by-product is the T-violating version of the Hauser--Feshbach expression involving a single mixing parameter. The relationship of this parameter to the mixing interaction strength is precisely clarified, and an approximate analytic relation is provided. Employing an extended exciton model with isospin properly incorporated, the statistical theory is applied to a comparative study of the photoalpha-particle reactions /sup 28/Si(..gamma.., ..cap alpha../sub 0/)/sup 24/Mg and /sup 30/Si(..gamma.., ..cap alpha../sub 0/)/sup 30/Mg in their giant dipole resonance regions. Although the former is isospin-forbidden, its energy-integrated experimental cross section is about twice that of the latter which is isospin-allowed. This discrepancy is explained.

• Research Organization: The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen O, Denmark
• OSTI ID: 5460585
• Journal Information: Ann. Phys. (N.Y.); (United States), Journal Name: Ann. Phys. (N.Y.); (United States) Vol. 107:1; ISSN APNYA
• Country of Publication: United States
• Language: English

Related Subjects

651415 -- Nuclear Properties & Reactions
A=20-38
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653003* -- Nuclear Theory-- Nuclear Reactions & Scattering
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ALKALINE EARTH ISOTOPES
ALPHA PARTICLES
CHARGED PARTICLES
CROSS SECTIONS
EVEN-EVEN NUCLEI
FLUCTUATIONS
GIANT RESONANCE
HAMILTONIANS
HAUSER-FESHBACH THEORY
INVARIANCE PRINCIPLES
ISOSPIN
ISOTOPES
LIGHT NUCLEI
MAGNESIUM 24
MAGNESIUM 30
MAGNESIUM ISOTOPES
MATHEMATICAL MODELS
MATHEMATICAL OPERATORS
NUCLEAR MODELS
NUCLEAR REACTIONS
NUCLEAR THEORY
NUCLEI
PARTICLE PROPERTIES
PHOTONUCLEAR REACTIONS
PRECOMPOUND-NUCLEUS EMISSION
QUANTUM OPERATORS
RESONANCE
SILICON 28 TARGET
SILICON 30 TARGET
STABLE ISOTOPES
STATISTICAL MODELS
SYMMETRY BREAKING
T INVARIANCE
TARGETS
UNIFIED MODEL
VARIATIONS