Scattered photons

Similarly, if the atom moves along -z it will scatter photons at a faster rate from the Mdj = -l-l transition. 

Fig. 6. Schematic illustration of the relationships of the original y-ray and the scattered radiations for Compton scattering where E is the energy of the incident photon, E is the energy of the recoiling electron, and E is the energy of the scattered photon.

Extinction Coefficient a measure of the ability of particles or gases to absorb and scatter photons from a beam of light a number that is proportional to the number of photons removed from the sight path per unit length. See absorption. Extinction Cross Section the amount of light scattered and absorbed by a particle divided by its physical cross section. 

Compton Effect—An attenuation process observed for x- or gamma radiation in which an incident photon interacts with an orbital electron of an atom to produce a recoil electron and a scattered photon whose energy is less than the incident photon. 

Compton profile. Furthermore the contribution of the multiple scattered photons to the measured spectra has to be taken into account (for example by a Monte Carlo simulation [6]). Additionally one has to take heed of the fact that the efficiency of the spectrometer is energy dependent, so the data must be corrected for energy dependent effects which are the absorption in the sample and in the air along the beam path, the vertical acceptance of the spectrometer and the reflectivity of the analyzing crystal. 

The scattered photon intensity, IS(E, P), from Li at a pressure P was estimated in the following way where E is the photon energy. First the X-ray intensity at ambient pressure without the Li sample is observed (i.e.the background), h E). The background h E) is assumed to be independent of pressure. Second the intensity including the Li sample is observed, I(E, P). It is assumed that P(E, P) has the following form,... 

Figure 17 Molar mass distributions of polystyrene in ethyl acetate obtained by dynamic light scattering (photon correlation spectroscopy, PCS) and TDFRS with short and long exposure time tp. The dashed curves represent the distribution as determined by SEC. Reproduced with permission from Rossmanith and Kohler [107]. Copyright 1996 American Chemical Society.

At room temperature the thermal population of vibrational excited states is low, although not zero. Therefore, the initial state is the ground state, and the scattered photon will have lower energy than the exciting photon. This Stokes shifted scatter is what is usually observed in Raman spectroscopy. Figure la depicts Raman Stokes scattering. 

A small fraction of the molecules are in vibrationally excited states. Raman scattering from vibrationally excited molecules leaves the molecule in the ground state. The scattered photon appears at higher energy, as shown in Figure lb. This anti-Stokes-shifted Raman spectrum is always weaker than the Stokes-shifted spectrum, but at room temperature it is strong enough to be useful for vibrational frequencies less than about 1500 cm 1. The Stokes and anti-Stokes spectra contain the same frequency information. 

Cylindrical lead collimators with 10 mm thick walls and a clear aperture of about 10 mm diameter were placed between the pin-hole and the X-ray output window of the main chamber to reduce scattered photon noise inside the vacuum chamber. Also, a set of magnets (with typical magnetic field strength of about 1 T) were placed inside each tube to stop high-energy electrons. All these measures were adopted to reduce as much as possible X-rays produced... 

Within this approximation, at least half of the photons that contribute to reflectance of a semi-infinite layer have been scattered only once. On (5-irradiation this part of photons is reflected from the illuminated surface with an exponential time profile Jo(t) = 2 xNoSac-exp(-(Sa + K )c-t), where N, is the number of incident photons at t = 0. Considering a weakly absorbing and not too strongly scattering sample (A = 1 cm S 102 cm-1), the decay time of the single-scattered photons is in the order of r = 500 fsec. The second half of photons is multiply scattered and decays... 

Figure 25 Schematic illustration for a system based on energy-dispersive coherent X-ray scatter (CXRS). Observation of the scattered photons is restricted to a fixed angle via a pinhole collimator. The spectrum from a highly energy resolving detector will show peaks at particular energies that are characteristic of the polycrystalline target. Computerized identification techniques can be used to identify the target substance.

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

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