High-energy radiation and matter

The radiation-induced conductivity of nonpolar liquids is of fundamental and practical interest. Ionization is one of the primary processes in the interaction of high-energy radiation and matter. From the measurement of the radiation-induced conductivity, information on the spatial distribution of the ionization events along the path of the ionizing particle can be obtained. From a practical point of view, liquid ionization chambers have received increasing attention in high-energy physics and medical physics where they supplement other types of detectors. 

One of the fundamental interactions between high-energy radiation and matter is the process of ionization. Ionization leads to the formation of charge carriers and to an increase in the electrical conductivity of the material. The spatial distribution of the ionization events is strongly dependent on the quality of radiation. We may distinguish the types of radiation by the way the ionization process is accomplished  

In liquids with sufficiently high electron mobilities, the ionization electrons produced in the track of an individual particle or quantum can be detected separately. An advantage of this method is the fact that once the ionization electrons have escaped into the bulk of the liquid, no losses due to volume recombination with positive charge carriers occur. A disadvantage is, however, that electron attachment to electronegative impurities influences the electron signal. This is the foimdation of the application of liquids in electron pulse chambers (see Section 9.2). 

The other fundamental interaction of particles or quanta with matter is the process of excitation of atoms or molecules. Platzman gave the following energy-balance equation (Myers, 1968)  

For the ratio W/Ig g one finds values close to 1.7 for noble gases, while for molecular gases the values lie between 2.1 and 2.6. In other words, roughly one half of the energy lost by the particle is converted into ionization, the other half into excitation. 

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