Ionization losses

The occurrence of fine structures has already been noted in the sections on spectral information and ionization losses (Sects. 2.5.3 and 2.5.3.2). In the following text some principal considerations are made about the physical background and possible applications of both types of feature, i. e. near-edge and extended energy-loss fine structures (ELNES/EXELFS). A wealth of more detailed information on their usage is available, especially in textbooks [2.171, 2.173] and monographs [2.210-2.212]. 

The light elements present in cosmic rays are partly thermalized, i.e. brought down to low velocities by ionization losses, and thus make a minor contribution to their abundance in the ISM (perhaps about 20 per cent). The main source is usually thought to come from reactions of cosmic-ray protons and a-particles with stationary nuclei of He, C, N and O in the ISM. 

Figure 2.5 Schematics of the concepts for (a) ionization-loss stimulated Raman spectroscopy (ILSRS), where resonant two photon ionization of the molecular parent, follows the depletion of ground state reactant species as a result of SRS and (b) VMP, where preexcited molecules are dissociated and the ensuing H photofragments are probed by (2 -I-1) resonantly enhanced multiphoton ionization. Reproduced with permission from Ref. [86]. Copyright (2009) AIP Publishing LLC.

The high energy primary cosmic rays produce many secondary neutrons and protons which in turn are responsible for most of the spallation reactions resulting in radionuclide production in the atmosphere. The formation of these radionuclides occurs at reaction thresholds of 10-40 M.e.v. Because of local ionization losses the secondary protons lose their... 

The Influence of the State of Aggregation on the Ionization Losses of Fast Charged Particles... 

Although the actual form of f(w, q) is different from formula (4.27), the latter leads to reasonable results when we use it to calculate the cross sections of inelastic collisions and the ionization losses.120 As one of the reasons for using approximation (4.27), one can consider the fact that the data concerning the Bethe surfaces for molecules are very scant, while there is extensive information about the optical oscillator strengths of molecules both in the discrete and in the continuous regions of the spectrum (see Refs. 119 and 121). 

Thus, the ionization losses supply the main part of the energy absorbed by the medium and are responsible for most of radiation effects. There are a large number of theoretical and experimental studies of ionization losses [see, for example, the monographs, Refs. 148, 154-156, and the reviews, Refs. 113 and 157], so here we will discuss only some of the aspects of the problem. 

Following from formula (4.54), the transfer of energy on excitation of molecules has a noticeable probability even in the case where the impact parameter is much greater than their size d. Since the intermolecular spacings in a condensed medium are of order of d, a charged particle interacts with many of its molecules. The polarization of these molecules weakens the field of the particle, which, in its turn, weakens the interaction of the particle with the molecules located far from the track. This results in that the actual ionization losses are smaller than the value we would get by simply summing the losses in collisions with individual molecules given by formula (5.1). This polarization (density) effect was first pointed out by Swann,205 while the principles of calculation of ionization losses in a dense medium were developed by Fermi.206... 

As in the case of fast electrons, the main contribution to energy losses of heavy charged particles (ions) comes from ionization losses (see Section V), which are responsible for most of the radiation-chemical effects. Therefore, we consider here only the structure of that part of an ion s track where the ionization losses are dominating. The role of elastic interaction between ions and atoms of the medium, which becomes essential only at the end of the ion s track, is not considered in this section. 

One of the characteristics of radiation considered in radiation chemistry and in radiobiology is the linear energy transfer (LET). For fast charged particles the LET practically equals the ionization losses (or polarization losses, in condensed media) and is given by the formulas for the stopping power presented in Section V.A. 

As is mentioned in Sect. 2.2, a discussion of de-ionization processes in the Earth s atmosphere would be incomplete without a mention of the r le of aerosols. The attachment of ions to aerosols in the stratosphere and troposphere has been considered by several workers213. It is clear that their presence will enhance the loss of ions from the gas phase at a rate dependent on the nature, size and number density of the particles, and so this process, which could be the dominant ionization loss process, must be considered along with gas phase ionic recombination in detailed atmospheric de-ionization rate calculations. 

Finally, it should be mentioned that channelling effects (the steering of charged particles in open regions in the lattice) could reduce the specific ionization loss. 

The interaction of ionizing electromagnetic radiation with matter is different from the processes previously mentioned, and the concept of ranges and specific ionization loss cannot be applied. Only the three most important absorption processes are considered the photoelectric effect, the Compton effect, and the pair-production effect. The corpuscular description of electromagnetic radiation is the most appropriate for these effects, as one photon in a well-collimated beam of photons disappears at each interaction. The attenuation of the photon beam can be described by a simple exponential law... 

Structural Studies. In a number of communications,22-26 correlations have been sought between both the spectroscopic and chemical properties of the various carbon allotropes and their structures. Thus, an electron-energy-loss spectroscopic study22 of diamond, graphite, and amorphous carbon has shown that the differences in the X-shell ionization loss spectra of the three allotropes (Figure 1) might be the basis of a technique for distinguishing... 

Figure 1 K-Shell ionization-loss spectra of diamond, graphite, and amorphous carbon...

Ionization losses, multiple scattering, and the deflection in the local magnetic field are considered. The decay of particles is simulated in exact kinematics, and the muon polarization is taken into account. 

A silver layer 0.3-1.5 nm thick was deposited on boron-doped diamond and thermally annealed until it disappeared. In contrast to other metals, no evidence for intermixing, graphitization or carbide formation was observed at the interface by Auger electron spectroscopy, ionization loss spectroscopy and low energy electron diffraction263. It was shown by Auger electron spectroscopy that no Ag—Si bonds are formed at the interface of silver deposited on or annealed with silica, in contrast to Ti deposited on or annealed with silica264. 

Chloro-1- butene will not undergo any appreciable resonance stabilization upon ionization (loss of Cl ) therefore the positive charge will not be stabilized by electrons from the double bond. 

A mass spectrometer causes atoms to lose electrons, a process called ionization. Loss of an electron means that the positive charge of the protons in the nucleus is not balanced by the remaining electrons, and the atom is now positively charged... 

They employed a magnet to determine the momentum of the charged particles and a proportional counter to measure the ionization loss of the particles. Combining these two pieces of information one obtains the mass of the particle and its energy. They observed protons, deuterons, and tritons were being emitted from the target. 

The DAPS spectra of La and Ce have been compared with ionization loss spectroscopy (ILS) spectra under various oxygen exposures. These two spectroscopies may respond in different ways to the changing chemical environment if Coulomb correlation effects are not negligibly small. The DAPS and ILS spectra for lanthanum are shown in... 

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