Inhibition and quenching

In polymer systems, positron chemistry can occur if the e+ is able to attach itself to a particular atom or group. Halogenated polymers, radicals and certain electron rich unsaturated structures have the capability of forming stable species of the form (e+,R ), with free positrons. These processes can lead to quenching and inhibition of Ps formation. 

When inhibition of positronium formation occurs, it is seen as a decrease in the o-Ps intensity, while quenching of o-Ps, as a result of chemical reactions, will shorten the o-Ps lifetime (x3). While quenching and inhibition of positronuim have been extensively studied in solution (see Chapter 5) it is a factor that has often been overlooked in polymer studies. There are numerous examples of inhibition and quenching effects in polymers [42, 80-82] 

In the case of quenching the reduction (shortening of the o-Ps lifetime) is explained by the chemical reaction of positronium and the quenching species (which in many cases are additives present in the polymer matrix). The chemical rate constant for the reaction between the Ps and quenching species can be expressed in terms of the concentration of the quenching species [M], and it is found that it can be described by pseudo-first order kinetics as [42, 80]  

Clearly in any polymer studies the possibility of positronium chemistry influencing the lifetime parameters needs to be considered. Once again the in- 

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Cohen SG, Sherman W. Inhibition and quenching of the light induced reduction of benzophenone to benzopinacol and to benzhydrol. J Am Chem Soc 1963 85 1642-1647. 

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