Stopping ionizing radiation

Stopping power is proportional to specific ionization. Radiation detection terms discussed in this chapter are summarized below. 

Fig. 5.16. Penetrating powers of ionizing radiations a-particles can be stopped by paper, p-particles can be stopped by aluminum, y-radiation is weakened by lead, but is never greatly totally blocked neutrons will pass through lead, but will be stopped by thick wax or concrete.

AIN ceramics reveals luminescence under exposure of radiation of different types - a and p beams, y. X-rays, and UV light. In this paper, we will pay attention mostly to properties of luminescence produced by UV light irradiation, as well as stop briefly on luminescence properties produced by ionizing radiation, which potentially can be used in dosimetry. The experimental results mentioned in this chapter are described in detail in our previous works [27—41]. 

Alpha Particles Alpha particles have the same structure as the nuclei of helium atoms two protons and two neutrons. Relative to other forms of ionizing radiation, alpha particles are large. They have little penetrating power. A piece of paper or the outer layer of skin can stop them. 

Prof. Szwarc also contributed to the understanding of mechanisms of cationic polymerizations. In addition to the previously mentioned study of the cationic polymerization of styrene initiated by trifluoroacetic acid, he developed novel methods of initiation of cationic polymerization, e.g., the initiation of cationic polymerization by transfer of Cl " and N02 ions, and initiation by electron-transfer. In cooperation with deSorgo and David Pepper, he carried out the first stop-flow study of cationic polymerization that demonstrated the formation of the positive polystyryl cation and allowed its spectrum to be recorded. This work was published in J.C.S. Chem. Comm. 419, (1973). He was the first to point out that cationic polymerization induced by ionizing radiation is propagated by free cations [Makromol. Chem. 35a. 123 (I960)]. 

Of the types of ionizing radiation, alpha particles are the least penetrating—paper and skin will ordinarily stop alpha particles. 

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