Preequilibrium γ rays with angular momentum coupling

A spin-dependent expression is suggested for the emission rate of preequilibrium γ rays in the framework of the exciton model. The single-particle picture as well as the Brink-Axel hypothesis are adopted and the angular momentum coupling is treated in detail. The approach is consistent with the usual equilibrium γ emission rate and it also elucidates earlier nonspin preequilibrium results. The expression is completed by a fully spin-dependent formulation of the exciton model. As an illustrative example, the primary γ ray spectrum of the /sup 56/Fe(n,γ) reaction at 14.6 MeV is analyzed. The impact of the angular momentum conservation on the γ ray spectrum as well as the nucleon emission is rather small. The preequilibrium γ emission is dominated by Δn = 0 transitions between levels with low spins in the very first n-exciton stages of the reaction