Irradiation angle

X-rays have a large penetration depth. In order to obtain a sufficiently intense signal from the surface layer the incident beam is applied under a very small angle (see exercise 8.4). Typical vertical irradiation angles a are 0.1°, which leads to penetration depths of 5 nm. With a wavelength of a few A (often the Cu-Ka line with A = 1.54 A, is used) the X-rays are sensitive enough to analyze monolayers. Also thicker layers can be analyzed. Widely used X-ray techniques are X-ray reflection (XR) and diffraction (XD), which provide different information on thin films [585,599,601],... 

The irradiation angle and sample geometry can have a large effect on the observed spectrum. 

Cheang-Wong, J.C. Morales, U. Resendiz, E. Lopez-Suarez, A. Rodriguez-Femandez, L. 2008. Dependence of the MeV ion-induced deformation of colloidal silica particles on the irradiation angle. Nuclear Instruments and Methods in Physics Research, Section B, 266(12-13) 3162—3165. 

NEXAFS experiments were carried out at the National Synchrotron Light Source (NSLS), Brookhaven National Lab (New York), on Exxon Beamline U1A in the partial electron yield mode for various irradiation angles between normal and grazing incidence. To compensate for the severe charging of the samples. 

Spectral Filters It is common to use cooled filters, sometimes at a nonnormal angle of irradiance, but most of the readily available spectral curves are taken at room temperature and normal irradiance. The correction of filter data for temperature and irradiance angle is discussed briefly in Chapter 14, but actual measurements should be used whenever possible. In any case, see that these effects have been considered in all radiometric calculations. 

Cox et al. (1975) Infrared Reflectance of Silicon Oxide and Magnesium Flouride Protected Aluminum Mirrors at Various Angles of Irradiance from 8 to 12 pm by J. T. Cox, G. Hass, and W. R. Hunter, Appl. Opt. 14, 1247. Poor reflectance for large irradiance angles for 8 to 12 pm otherwise, high reflectance at normal irradiance and for other wavelengths. 

There are two ways that this oblique incident method can be carried out. The method of double polarized UV exposure with different polarization and irradiation angles was first proposed by limura et al. [3] (Figure 3.2). 

Disadvantages. The magic angle must be extremely stable and accurately set. The spiiming speed must show good stability over the duration of the experiment. The probe needs to be accurately tuned and careful correction for irradiation and detection variations with frequency, and baseline effects are necessary. The gain... 

This simulation can be achieved in terms of a source—sink relationship. Rather than use the gas concentration around the test object as a target parameter, the test object can be surrounded by a sink of ca 2-7T soHd angle. The solar panel is then maintained at its maximum operating temperature and irradiated by appropriate fluxes, such as those of photons. Molecules leaving the solar panel strike the sink and are not likely to come back to the panel. If some molecules return to the panel, proper instmmentation can determine this return as well as their departure rates from the panel as a function of location. The system may be considered in terms of sets of probabiUties associated with rates of change on surfaces and in bulk materials. 

In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiate a specimen, and the emitted fluorescent X rays are analyzed with a crystal spectrometer and scintillation or proportional counter. The fluorescent radiation normally is diffracted by a crystal at different angles to separate the X-ray wavelengths and therefore to identify the elements concentrations are determined from the peak intensities. For thin films XRF intensity-composition-thickness equations derived from first principles are used for the precision determination of composition and thickness. This can be done also for each individual layer of multiple-layer films. 

Reflectometry is a useful probe with which to investigate the structure of multilayers both in self-supporting films and adsorbed on surfaces [51]. Specular X-ray reflectivity probes the electron density contrast perpendicular to the film. The X-rays irradiate the substrate at a small angle (<5 °) to the plane of the sample, are reflected, and are detected at an equal angle. If a thin film is present on the surface... 

Table 7 reveals that the grafting of TAC onto PE decreases the equilibrium contact angles of water and formamide from 92° to 65° and from 75° to 53°, respectively. This decrease is a function of the monomer level and the irradiation dose. At a fixed irradiation dose of 15 Mrad, variation of the TAC level from 0.5 to 3 parts causes a reduction in the contact angles of water by 13° (from 88° to 75°) and of formamide by 11° (from 72° to 61°). This is due to the fact that the concentration of... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

Thus, the process of PAN transformation under the effect of IR radiation proceeds with considerable self-acceleration. The irradiation of uniaxially oriented PAN films gives a polymer with a distinct anisotropy of optical properties, dichroism in the visible spectral region in particular. Figure 8 presents dichroism curves [D =/(X)] at various angles (ip) between the polarization plane and the orientation axis. The same figure shows the dependence D =f(uniaxially oriented film. 

Fig. 8. Dichroism of electronic absorption spectra of oriented and nonoriented PAN films after IR irradiation, (a) Dependence of optical density ( >) on the wavelength for various values of (angle between film orientation axis and light polarization plane).

Depth of EB penetration The depth of penetration of energetic electrons into a material at normal angle of incidence is directly proportional to the energy of the electrons and inversely proportional to the density of the material [49,50]. The depth is expressed as a product of penetration distance and the density of the material (i.e., 1 g/cm = 1 cm X 1 g/cm ). The radiation energy and thus the type of electron accelerator to be used are dependent on the required penetration depth, the density of the irradiated material, and the chosen irradiation system. If one measures the density (d) in gram per cubic centimeter (g/cm ) and the layer thickness (T) in millimeter (mm), one can determine the radiation energy ( ) necessary for optimal homogeneity from [40] ... 

The radioactive source need not aiways be introduced into the body. Inoperable brain tumors can be treated with y rays from an extemai source, usuaiiy a sampie of cobait-60. The patient is placed in a position where the y-ray beam passes through the tumor. The patient is moved so that the y rays irradiate the tumor from several angles. In this manner the tumor receives a much higher dose of radiation than the dose received by any surrounding tissues. 

What happens in three-spin systems when the A-B-C angles 0 are 180° and 78°, respectively, = rgc = 1, and spin A is irradiated ... 

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