Cross sections absorption

Computer software codes are available to deconvolute PIXE spectra and to calculate peak areas with accuracy, so that absolute amounts of elements present in the specimen may be derived. With a beam of 5 mm diameter incident on a thin organic specimen on a thin backing foil, trace elements can be detected at picogram levels. The x-ray production cross-sections, absorption coefficients and the various... 

Scattering cross section, absorption cross section... 

Absorption Cross Section. Absorption cross section a "(A) is related to absorbance ABS(A) by equation (11). 

Interaction of an EM field with a nanostructured metal surface also strongly influences other optical phenomena, namely absorption and luminescence. Surface-enhanced infrared absorption (SEIRA) of monolayers of benzoic acids on thin Ag island films was first observed in 1980s (Hartstein et al. 1980). The EM mechanisms is attributed to a local field enhancement and, correspondingly, to an enhancement of the absorption cross-section. Absorption can be enhanced generally by a factor of 10 -10 (Osawa 2001 Aroca 2006) and SEIRA is used as a complementary technique to SERS in some cases (Aroca 2006). 

Spectral absorption (transmission) lines are not monochromatic, due to which physical values characterizing transitions of the molecular system from one quantum state to another are also energetically diffused. Therefore, any spectral quantity F (absorption cross section, absorption coefficient, Einstein coefficients, and others) can be of three types F, is the spectral value, Fq is the maximum value corresponding to the frequency Hq, and F = 6F dn is the integral value for the spectral line. The integral and spectral values are related by the following relationship ... 

To describe quantitatively the interactions of bombarding particles with atomic nuclei the concept of cross section was introduced. In this sense the term "cross section" is a measure of the probability of occurrence of a given process under certain conditions. To illustrate the concept of nuclear cross section, it can be visualized as the cross-sectional (or target) area presented by a nucleus to an incident neutron. If we further visualize the nucleus as a sphere of radius r cm, and think of the neutrons as point projectiles, then the target area or cross section o of each nucleus is a = 7T r cm. This simple picture illustrates only one type of cross section, the geometrical, and considers only collisions of neutrons with target nuclei. But it serves to derive a formula for cross section that can be extended to any kind of interaction of neutrons with atomic nuclei. Today, there are experimental values for many kinds of cross sections (absorption, scattering, activation, etc.) for different materials, and several types of each (microscopic, macroscopic, atomic, nuclear, differential). 

AF, Atmospheric fate, mechanisms, and final products of atmospheric reactions CS, Cross sections, absorption (a) for the compound... 

One more application area is composite materials where one wants to investigate the 3D structure and/or reaction to external influences. Fig.3a shows a shadow image of a block of composite material. It consists of an epoxy matrix with glass fibers. The reconstructed cross-sections, shown in Fig.3b, clearly show the fiber displacement inside the matrix. The sample can be loaded in situ to investigate the reaction of matrix and fibers to external strain. Also absorption and transmission by liquids can be visualized directly in three-dimensions. This method has been applied to the study of oil absorption in plastic granules and water collection inside artificial plant grounds. 

The transition probability for absorption of two photons can be described in tenns of a two-photon cross section 5 by... 

We have seen that the strength of Raman scattered radiation is directly related to the Raman scattering cross-section (Oj ). The fact that this cross-section for Raman scattering is typically much weaker than that for absorption (oj limits conventional SR as a sensitive analytical tool compared to (Imear) absorption... 

The exponential decay of the A population corresponds to a Lorentzian line shape for the absorption (or emission) cross section, a, as a fiinction of energy E. The lineshape is centred around its maximum at E. The fiill-width at half-maximum (F) is proportional to... 

Figure B3.4.7. Schematic example of potential energy curves for photo-absorption for a ID problem (i.e. for diatomics). On the lower surface the nuclear wavepacket is in the ground state. Once this wavepacket has been excited to the upper surface, which has a different shape, it will propagate. The photoabsorption cross section is obtained by the Fourier transfonn of the correlation function of the initial wavefimction on tlie excited surface with the propagated wavepacket.

Beryllium is used in nuclear reactors as a reflector or moderator for it has a low thermal neutron absorption cross section. 

Commercial-grade zirconium contains from 1 to 3% hafnium. Zirconium has a low absorption cross section for neutrons, and is therefore used for nuclear energy applications, such as for... 

Because the element not only has a good absorption cross section for thermal neutrons (almost 600 times that of zirconium), but also excellent mechanical properties and is extremely corrosion-resistant, hafnium is used for reactor control rods. Such rods are used in nuclear submarines. 

Thermal neutron absorption cross section. Simply designated cross section, it represents the ease with which a given nuclide can absorb a thermal neutron (energy less than or equal to 0.025 eV) and become a different nuclide. The cross section is given here in units of barns (1 barn = 10 cm ). If the mode of reaction is other than ( ,y), it is so indicated. 

Both microwave and millimetre wave radiation can be channelled in any direction by a waveguide made from metal tubing of rectangular cross-section, the dimensions depending on the frequency range. The absorption cell is also made from waveguide tubing. 

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