Average lifetimes and 3-to-2 photon ratio

For porogen loads up to 20% the relation is linear independent of the aperture placement. When the aperture is not in place (downward triangles) the same linear relation continues to a porogen load of about 35%. In the case of the apertured lifetime setup the slope changes to a lower value at about 20% and then remains constant to a porogen load of 50%. At higher loads the mean lifetime values drop sharply while the positronium fraction drops less sharply (open symbols). The trends are consistent with the onset 

The positronium fraction (F) for a given mean lifetime is F = tmean (71.5 1.2) l/ns. After this calibration, the 3-to-2 photon ratio can be related to a mean pore dimension. This may be premature because no data exist to date on the dependence of this relation on the concentrations of specific pore sizes, which will probably alter the slope. Given fixed pore generating and matrix materials (as in this case) the relation appears to be valid. 

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