Direct-Semidirect Thermal Neutron Capture Calculations

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A method for computing direct-semidirect (DSD) neutron radiative capture is presented and applied to thermal neutron capture on {sup 19}F, {sup 27}Al, {sup 28,29.30}Si, {sup 35,37}Cl, {sup 39,41}K, {sup 56}Fe, and {sup 238}U, 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 ... continued below

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10 p. (0.2 MB)

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Arbanas, G; Dietrich, F S & Kerman, A K December 20, 2005.

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A method for computing direct-semidirect (DSD) neutron radiative capture is presented and applied to thermal neutron capture on {sup 19}F, {sup 27}Al, {sup 28,29.30}Si, {sup 35,37}Cl, {sup 39,41}K, {sup 56}Fe, and {sup 238}U, 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 {sup 238}U with and without imposition of spherical symmetry. Direct capture for a spherically symmetric {sup 238}U was approximately 6 mb, while a quadrupole deformation of 0.215 on the shape of {sup 238}U 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 {sup 238}U 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 {sup 56}Fe(n,{gamma}). This will lead us to revisit the concept of doorway states in the particle-hole model.

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10 p. (0.2 MB)

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PDF-file: 10 pages; size: 0.2 Mbytes

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  • Presented at: Perspectives on Nuclear Data for the Next Decade, Bruyeres-le-Chatel, France, Sep 26 - Sep 28, 2005

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  • Report No.: UCRL-PROC-217859
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 891381
  • Archival Resource Key: ark:/67531/metadc875703

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  • December 20, 2005

Added to The UNT Digital Library

  • Sept. 21, 2016, 2:29 a.m.

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  • April 13, 2017, 3:05 p.m.

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Arbanas, G; Dietrich, F S & Kerman, A K. Direct-Semidirect Thermal Neutron Capture Calculations, article, December 20, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc875703/: accessed June 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.