Measurement backscattering factor

For accurate results, the backscattering factor should be measured for the actual geometry of the experiment. 

A point isotropic source is located at the center of a hemispherical 2tr counter. The efficiency of this detector tor the particles emitted by the source is 85 percent. The saturation backscattering factor is 1.5. The background is 25 + 1 counts/min. What is the strength of the source if 3000 counts are recorded in 1 min What is the standard error of this measurement ... 

A plastic scintillation detector was to be calibrated for absolute measurements of /3-radiation. For this purpose a 2.13 X 10 M TlCl3 solution was available with a specific activity of 13.93 iCi ml T1 emits iS-particles with 0.77 MeV. Of this solution 0.1 ml is evaporated over an area of exactly 0.1 cm on a platinum foil. The sample is counted in an evacuated vessel at a distaiKe of 15.3 cm from the detector, which has a sensitive area of 1.72 cm. The detector registers 2052 cpm with a background of 6 cpm. What is (a) the surface weight of the sample, (b) the backscattering factor, and (c) the detector efficiency for the particular /3 s ... 

In a LEISS spectrum vide infra), the backscattered intensity is plotted against Ei/Eq a high-intensity peak corresponds to a topmost atom of a given mass, and the relative intensities provide a measure of the relative surface concentrations. Since the atoms scatter with different intensities, sensitivity factors / for each element must be obtained by calibration. For example, for an alloy film consisting of Pt and Co, the surface concentrations Cp and Cco can be extracted from the following equations ... 

Ferrare R. A., Meffi S. H., Whiteman D. N., Evans K. D., Poellot M., and Kaufman Y. J. (1998b) Raman hdar measurements of aerosol extinction and backscattering 2. Derivation of aerosol real refractive index, single-scattering albedo, and humidification factor using Raman hdar and aircraft size distribution measurements. J. Geophys. Res. 103, 19673-19689. 

In order to determine the nearest neighbor interatomic distance and the Debye-Waller factor, the classical EXAFS fitting procedure was used. Since at ambiant pressure and room temperature krypton is a gas, the backscattering amplitude and the phase shift have been obtained from the data at 15.7 GPa where the lattice parameter was known from X-ray diffraction [32]. Only the variation of the Debye-Waller factor can be measured. 

The subject of relative and absolute measurements is presented in Chap. 8. The solid angle (geometry factor) between source and detector and effects due to the source and the detector, such as efficiency, backscattering, and source self-absorption are all discussed in detail. 

LEIS measurements result in an energy spectrum of the backscattered ions from the sample surface. The energy of scattered ions provides information on the mass of the surface atoms, which is directly related to their chemical identity. The cross-section, solid angle and transmission factor (the analyser acts as an energy filter, with transmission characteristics that depend on the mode of operation) are used for these calculations. 

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