Ps trapping in solids the free volume model

The sites where Ps can become trapped and decay in solids correspond to pre-existing voids, whether of intrinsic or extrinsic origin. A quantitative equation has been established, which has proven to be reliable in many cases, correlating X3 with the radius (R) of the supposedly spherical trap  

One of the most successful and popular applications of Eq.(10) relates to the determination of free volumes in polymers [68], 

Extensions of Eq. (10) to traps having a large size [69] or a cylindrical shape [70, 71] are available. 

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