The structure of tracks

It should be emphasised that, typically, 60% or more of the inelastic collisions result in ejection of electrons with energy 10 eV and as little 

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As a rule the radiation effect produced by any type of emission is a superposition of direct effects of the primary radiation and of the secondary (and even tertiary) radiation the latter induces. Consequently, if the radiation effect is mostly due to the effect produced by secondary (or tertiary) emission, the latter can be used instead of the primary radiation. As concerns the structure of tracks, such a simulation will be correct if the spatial distribution of chemically active particles in the irradiated volume remains close to the one produced by the primary source. 

However, in the case of a root cause analysis system, a much more comprehensive evaluation of the structure of the accident is required. This is necessary to unravel the often complex chain of events and contributing causes that led to the accident occurring. A number of techniques are available to describe complex accidents. Some of these, such as STEP (Sequential Timed Event Plotting) involve the use of charting methods to track the ways in which process and human events combine to give rise to accidents. CCPS (1992d) describes many of these techniques. A case study involving a hydrocarbon leak is used to illustrate the STEP technique in Chapter 7 of this book. The STEP method and related techniques will be described in Section 6.8.3. 

The importance of track structure, the migration of species, the role of oxygen, the study of model compounds and the use of pulse radiolysis techniques are discussed. 

The utilily of measuring lattice vibrations for obtaining information about zeolites has been widely demonstrated. Applications include determining the structure of zeobtes by the identification of the structural units present, measuring changes in the framework Si/Al within materials with the same zeolite structure and tracking the formation of zeolite during synthesis. 

The organization of this chapter is as follows. In the following section, Sec. 4.2, the elastic and inelastic interaction cross sections necessary for simulating track structure (geometry) will be discussed. In the next section, ionization and excitation phenomena and some related processes will be taken up. The concept of track structure, from historical idea to modern track simulation methods, will be considered in Sec. 4.4, and Sec. 4.5 deals with nonhomogeneous kinetics and its application to radiation chemistry. The next section (Sec. 4.7) describes some application to high temperature nuclear reactors, followed by special applications in low permittivity systems in Sec. 4.8. This chapter ends with a personal perspective. For reasons of convenience and interconnection, it is recommended that appropriate sections of this chapter be read along with Chapters 1 (Mozumder and Hatano), 2 (Mozumder), 3 (Toburen), 9 (Bass and Sanche), 12 (Buxton), 14 (LaVerne), 17 (Nikjoo), and 23 (Katsumura). 

The first of these factors reduces the complexity of the simulation, but the second has entirely the opposite effect as charge cycling events affect both the energy of the primary ion and its inelastic collision cross section. While the proximity of energy loss events does not affect the details of track structure simulation (at reasonable LET), it may cause significant complications in subsequent diffusion-kinetic calculations due to the (potentially unphysi-cally) high local concentration of radiation-induced reactants. 

Curved-arrow notation is also a very useful device with which to generate resonance structures. In this application it is truly a bookkeeping system. Since individual canonical forms do not exist but are only thought of as resonance contributors to the description of a real molecule, the use of curved-arrow notation to convert one canonical form to another is without physical significance. Nevertheless it provides a useful tool to keep track of electrons and bonds in canonical structures. For example, the structures of carboxylate resonance contributors can be interconverted as follows ... 

The tracks of alpha particles and of electrons ejected by X rays were first observed in Wilson chambers. Later the more advanced bubble and spark chambers were designed. Another type of detector, which is widely used for recording particle tracks, is one that fixes the changes in the structure of a medium when treated by certain chemical reagents. These are the photoemulsions and the different types of solid detectors.6... 

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