Interaction of high-energy radiation with matter

Interaction of High-energy Radiation with Matter 

Understanding the effects of ionizing radiation on the properties of plastics materials is important in nuclear engineering, space research, radiation processing, and radiation sterilization. 

The nuclei of Ni atoms that result from this decay are in an excited state and immediately emit t3vo y-rays of energies 1.332 and 1.173 MeV. The low-energy are absorbed by the Co housing and all the radiolytic effects result from the y-ray emission. 

Electron accelerators can deliver higher dose rates, whereas Co sources are characterized by a greater depth of penetration. 

A fast electron loses most of its kinetic energy by inelastic collisions with electrons from the medium, producing energetic secondary electrons. Depending on the energy of the radiation, many secondary electrons of decreasing energy wUl be 

2 INTERACTION OF HIGH-ENERGY RADIATION WITH MATTER 

Since they are the most generally used, only X-rays, 7-rays and electrons will be considered here. 

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Interaction of high energy radiation with matter... 

The subject of radiation chemistry includes the study of the chemical reactions that occur as a result of the interaction of high-energy radiation with matter. This has been dealt with in Chapter 2, Volume 3, but some relevant general remarks will provide an introduction to hydrocarbon radiolysis. 

This section deals with the fundamental nature of the interactions of high-energy radiations with matter, from the absorption of the radiations to the eventual establishment ofchemical equilibrium in the system. The process may bedivided into three stages which are illustrated in Fig. 1. 

Interaction of High-energy Radiations with Matter. 14... 

Elementary Processes of the Interaction of High-Energy Photons with Matter Table4.1 Denotations for high-energy photon radiations. 

The interaction of intense laser radiation with matter differs from that of conventional radiation sources. The high incident irradiances available with lasers can lead to a significant depletion of the initial level population. As a result, the optical absorption coefficient decreases as a function of the excitation energy and the absorbed energy tends towards a constant value. This so called optical saturation effect leads to a nonlinear dependence of the absorption signal on the light intensity. Because the amount of energy released by radiative and nonradiative relaxation processes... 

It is convenient at this stage to summarise the species that may be produced by the interaction of high energy ionising radiation with matter, though the evidence for their existence will be considered in detail in Section 2. 

Sensing of high energy radiation is performed either directly in the a-Si H film or using an intermediate converter material, as illustrated in Fig. 10.27. Direct detection requires a thick film, typically 10-100 im, because most ionizing radiation interacts weakly with matter. The converter material is usually a phosphor which absorbs the radiation and emits visible light. Thin a-Si H sensors are excellent detectors of such visible light. 

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