Notes:
In a “viscous flow” model the radiolysis electron moves at approximately the speed of sound and follows electric field “lines” in the direction of the vector sum of the muon's Coulomb field and the constant external field. This makes it easy to separate all space into a region where the electron will escape capture and another region from which it will inevitably be catured in DMF. Of course, this model corresponds to zero temperature; at finite T the capture region will be reduced further to the region where the binding energy to the muon is greater than kT. (Unlike for zero applied field, this region will not be spherical.)