Shielding factors, computation

The EFG parameters Vzz and described by (4.42a) and (4.42b) do not represent the actual EFG felt by the Mossbauer nucleus. Instead, the electron shell of the Mossbauer atom will be distorted by electrostatic interaction with the noncubic distribution of the external charges, such that the EFG becomes amplified. This phenomenon has been treated by Stemheimer [54—58], who introduced an anti-shielding factor (1 —y 00) for computation of the so-called lattice contribution to the EFG, which arises from (point) charges located on the atoms surrounding the Mossbauer atom in a crystal lattice (or a molecule). In this approach,the actual lattice contribution is given by... 

Burrows and Cohen used their solutions found with Maple to compute the dipole polarizabilities and shielding factors of a general ns state, obtaining results that improve upon recent accurate calculations reported by Montgomery [44] and by Laughlin [43]. 

The thermal-neutron self-shielding factor of the foil, a, is computed by diffusion theory. This factor is based upon an isotropic flux it is therefore implied that the foil was irradiated in a medium having good scattering properties for thermal neutrons. The calculation of the self-shielding factor is considered in Appendix C. 

This trend is consistent with those observed for both proton and carbon chemical shifts, with the proton on the most highly substituted carbon, and the carbon with the most alkyl substituents being the most highly deshielded. Computational work by Wiberg and Zilm has allowed identification of the factors that lead to the observed shielding trends that are observed for alkyl fluorides.1... 

The heat transfer rate can now be computed. First consider the radiation leakage through the shield coil. From the previous example, the factor of comparison between a tube bank and a plane, a = 0.74. 

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