Direct-Semidirect Thermal Neutron Capture Calculations [electronic resource].

Published: Washington, D.C. : United States. Dept. of Energy, 2005.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description: PDF-file: 10 pages; size: 0.2 Mbytes
Additional Creators: Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary

A method for computing direct-semidirect (DSD) neutron radiative capture is presented and applied to thermal neutron capture on ¹⁹F, ²⁷Al, {sup 28,29.30}Si, {sup 35,37}Cl, {sup 39,41}K, ⁵⁶Fe, and ²³⁸U, in support of data evaluation effort at the O.R.N.L. The DSD method includes both direct and semidirect capture; the latter is a core-polarization term in which the giant dipole resonance is formed. We study the effects of a commonly used ''density'' approximation to the EM operator and find it to be unsatisfactory for the nuclei considered here. We also study the magnitude of semidirect capture relative to the pure direct capture. Furthermore, we compare our results with those obtained from another direct capture code (Tedca [17]). We also compare our results with those obtained from analytical expression for external capture derived by Lane and Lynn [3], and its extension to include internal capture [7]. To estimate the effect of nuclear deformation on direct capture, we computed direct thermal capture on ²³⁸U with and without imposition of spherical symmetry. Direct capture for a spherically symmetric ²³⁸U was approximately 6 mb, while a quadrupole deformation of 0.215 on the shape of ²³⁸U lowers this cross section down to approximately 2 mb. This result suggests that effects of nuclear deformation on direct capture warrant a further study. We also find out that contribution to the direct capture on ²³⁸U from the nuclear interior significantly cancels that coming from the exterior region, and hence both contributions must be taken into account. We reproduced a well known discrepancy between the computed and observed branching ratios in ⁵⁶Fe(n,γ). This will lead us to revisit the concept of doorway states in the particle-hole model.

Report Numbers

E 1.99:ucrl-proc-217859
ucrl-proc-217859

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Note

Published through SciTech Connect.
12/20/2005.
"ucrl-proc-217859"
Presented at: Perspectives on Nuclear Data for the Next Decade, Bruyeres-le-Chatel, France, Sep 26 - Sep 28, 2005.
Dietrich, F S; Kerman, A K; Arbanas, G.

Funding Information

W-7405-ENG-48

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