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

Journal Article · Tue Sep 06 00:00:00 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), Vol. 107:1
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
PHOTONUCLEAR REACTIONS
PRECOMPOUND-NUCLEUS EMISSION
SILICON 28 TARGET
SILICON 30 TARGET
T INVARIANCE
SYMMETRY BREAKING
ALPHA PARTICLES
CROSS SECTIONS
FLUCTUATIONS
GIANT RESONANCE
HAMILTONIANS
HAUSER-FESHBACH THEORY
ISOSPIN
MAGNESIUM 24
MAGNESIUM 30
STATISTICAL MODELS
UNIFIED MODEL
ALKALINE EARTH ISOTOPES
CHARGED PARTICLES
EVEN-EVEN NUCLEI
INVARIANCE PRINCIPLES
ISOTOPES
LIGHT NUCLEI
MAGNESIUM ISOTOPES
MATHEMATICAL MODELS
MATHEMATICAL OPERATORS
NUCLEAR MODELS
NUCLEAR REACTIONS
NUCLEAR THEORY
NUCLEI
PARTICLE PROPERTIES
QUANTUM OPERATORS
RESONANCE
STABLE ISOTOPES
TARGETS
VARIATIONS
653003* - Nuclear Theory- Nuclear Reactions & Scattering
651415 - Nuclear Properties & Reactions
A=20-38
Theoretical- Nuclear Reactions & Scattering- (-1987)