Shielding factor

Diamagnetic shielding factor, spherical water 1 + crCHjO) 1.000 025 64(7) ... 

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... 

R. M. Mahbubar, Y. Michihiro, K. Nakamura, and T. Kanashiro, LDA Studies on Polarizabilities and Shielding Factors of Ions in Fluorite Structure Crystals, Sol. St. Ionics, 148,227 (2002). 

The time factor is the duration of exposure, with the assumption that the shorter the exposure time, the less likely it is that an individual will suffer an ill effect. The distance factor is the physical separation (e.g., in feet or miles) between an individual and the location of the terrorist event. The shielding factor refers to physical barriers between an individual and hazardous substances emanating from the attack location. These three factors are discussed in detail below, along with general rules for minimizing exposure. 

Shielding in this context refers to placement of a physical barrier between an individual and hazardous substances emanating from contaminated materials. In the field of radiation protection, shielding typically refers to a barrier that reduces radiation levels. The term is used in a broader sense here to refer to any physical barrier that reduces or eliminates exposure to a hazardous substance. Consider three rules of thumb for the shielding factor ... 

The calculations show that the central contribution to the EFG, due to the valence electrons, is shielded rather than antishielded, but the effect is less pronounced. The shielding factor R is the density-weighted average of y(r), <7( ) "3>core,vaience/core,valence, where the average is to be taken separately over the core and valence shells, depending on the shell in which polarization is induced. 

If the electron density were known at high resolution, the antishielding effects would be represented in the experimental distribution, and the correction in Eq. (10.31a) would be superfluous. However, the experimental resolution is limited, and the frozen-core approximation is used in the X-ray analysis. Thus, for consistency, the Rcore shielding factor should be applied in the conversion of the... 

X-ray EFG values to spectroscopic splittings. But the polarization of the valence shell is at least in part accounted for in the aspherical multipole description. To the extent that the model is sufficiently flexible, the shielding factor Rva,ence is not needed, and the correction equation becomes... 

Applications of the core shielding factors in X-ray studies of pyrite, Fe(Il) phthalocyanine, and bis(pyridine)(meso-tetraphenylporphinato)iron(II) generally improve agreement with spectroscopic values (Su and Coppens 1996). 

The factor No/02/3 is called the shielding factor it will be smallest for thin-gap, thin-ring electrodes. 

Compton wavelength of neutron Compton wavelength of proton Diamagnetic shielding factor, spherical H20 molecule Electron g factor Electron magnetic moment Electron radius (classical) Electron rest mass... 

Figure IS Shielding factor cr(r) in the ground state of helium as a function of the distance r from the nucleus. a(r) is the difference between the charge Z = 2 of the bare nucleus and the effective charge ZtH seen by one of the electrons due to the presence of the other electron. indicates the mean distance of the ls-electron from the nucleus ( radius of the Is shell). Data from [WLi35], cf [BSa57] with ZM = Z9.

The quantity which characterizes the shielding effect of /i-metal boxes is called the shielding factor S. It is defined by the ratio of outer to inner field strength (see Fig. 10.7),... 

For a static magnetic field and a sphere with inner and outer diameters, D and D0, respectively, this shielding factor can be calculated giving [VAC75]... 

The shielding factor, a, is related to the chemical shift in parts per million ... 

D0, respectively, this shielding factor can be calculated giving [VAC75]... 

In fact (N0f 213) < 1 and the term in brackets, the shielding factor, is always positive. The shielding factor is the maximum reduction in the detector electrode current that can be caused by the generator electrode its use is to remove an unwanted electroactive species from solution that interferes with the reaction under study. To maximize the reduction in current (minimize the shielding factor) we want an electrode geometry such that (A/o/3-2/3)—> 1, which corresponds to a very small interelectrode gap, (r2 — rf), and a thin detector electrode. 

This is the result first obtained by Ramsay [21]. We note finally that an important quantity, measured in isotropic liquid phase n.m.r. studies, is the average shielding factor aav. This is given by the trace of the shielding tensor a, i.e. 

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