Backscattering coefficient

Fig. 7-2 Vertical profiles of physical (temperature, dew point, and backscatter coefficient) and chemical (ozone, sulfur dioxide) variables near Scranton, PA during the afternoon of 20 July 1978. (Modified with permission from P. K. Mueller and G. M. Hidy (1982). "The Sulfate Regional Documentation of SURE Sampling Sites", EPRI report EA-1901, v. 3, Electric Power Research Institute.)...

The calculation of backscatter coefficients via the approach outlined above is mathematically complex. Heidenreich 44) developed a simple empirical backscatter model which is applicable to resist exposure being based on the direct observation of chemical changes produced by backscat-tered electrons at different accelerating voltages on several substrates. The model is independent of scattering trajectory and energy dissipation calculations and is essentially a radial exponential decay of backscatter current density out to the backscatter radius determined by electron range. 

Here, ry is the backscatter coefficient for the substrate and the line input dose which is equal to i /x. The Gaussian beam radius in the resist at penetration z is... 

For phosphors based on zinc sulfide (ZZn = 30, Zs = 16 hence, ZZnS = 23) this gives a backscattering coefficient ri 0.27. This means that 27 % of the energy supplied is not available for luminescence. The effect of the electron energy on backscattering is described in [5.309],... 

Positron transmission and scattering measurements using superposition of annihilation line shapes backscatter coefficients. Phys. Rev. A 7 135-145. 

Particle- and energy-backscattering coefficients of light ions from solids. Distributions of energy and angle of scattered particles also are included (282 sets). 

The intensity of the electrons backscattered from a particular region of a specimen depends approximately on the mean atomic number of the material of which that region is composed more precisely, it is represented by the backscattering coefficient, q, which may be calculated from the formulae ... 

Compositional contrast refers to the variation in gray levels in an SEM image that correspond to variation in chemical composition in a specimen. An image formed by BSEs exhibits very useful compositional contrast if the specimen consists of more than one chemical element. The origin of compositional contrast arises because the capability of BSEs to escape from the specimen depends on the atomic numbers of the specimen atoms. The backscatter coefficient (rj) characterizes such capability. 

Figure 4.15 Backscatter coefficient as a function of atomic number of specimen atoms. (Reproduced with kind permission of Springer Science and Business Media from J.I. Goldstein et al, Scanning Electron Microscopy and X-ray Microanalysis, 2nd ed., Plenum Press, New York. 1992 Springer Science.)...

M. Stramska, D. Stramski, B.G. Mitchell, C.D. Mobley (2000). Estimation of the absorption and backscattering coefficients from in-water radiometric measurements. 

For the altimetric data the methodology is based on the analysis of time and space evolution of observations in the space of two parameters (a) backscatter coefficient... 

Lidar, Aerosol, Backscattering ratio, Backscattering coefficient. Extinction, Backtrajectory Introduction... 

Vertical distribution of aerosols extinction coefficient, backscattering coefficient, single scattering albedo. 

Figure 1. Monitoring of integral backscattering coefficient in the height range 15-30 km.

Backscatter coefficient The number of backscattered electrons emitted from a specimen... 

The backscattered light depends on the structure of the sample material. For instance have cancer cells in a biological tissue a different backscattering coefficient than normal cells. They cause a different amplitude and phase of the backscattered light. 

At high energies (E>5keV) the backscatter coefficient, t], hardly varies with E and shows a monotonic increase with Z. At low energies (Econtrast reversal occurs. 

This is a consequence of the strongly decreased elastic scattering cross-section for the high-atomic number materials at low energies. As shown by Re-imer, these effects can only be predicted by extensive quantum mechanical scattering cross-section calculations based on the partial wave expansion method. For a compound material the backscatter coefficient can be obtained by weighting the elemental backscatter coefficients with their mass fractions, c according to eqn [6] ... 

Figure 39. Backscattering coefficient and secondary electron emission (Eq = 30 keV) as a function of atomic number Z (from Seidel, Wittry).

When rocking an incident electron beam, the backscattering coefficient is modulated by a few percent. This results in an electron channeling... 

The form of Eq. 3.10 is nearly identical to that of Eq. 3.5 with the exception of two additional terms, Xi the Auger transition probability and r the secondary ionization, or backscatter coefficient. Eor simplicity, it is typical to combine a and X into a single term that can be considered on a relative scale by a term knows as the relative sensitivity factor (RSE), Si. As is the case with XPS, these factors are also tabulated by the instmment manufacturer and are specific to the particular... 

The probability of elastic scattering varies strongly with atomic number, as Z, but the probability of backscattering, rj, varies much less. For 20keV electrons it is 0.06 for carbon and increases to 0.5 for silver [68] (shown in Fig. 3.21 of [38]). If the scattering is very efficient, in a short distance into the specimen, half the electrons will be going forward and half backward. Thus the backscattering coefficient saturates near 0.5 there is only a few percent difference between values for silver and uranium. 

There is generally little change in backscattering coefficient with beam voltage. This may... 

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