A computer model of the formation of molecular excited states in irradiated alkane solutions was applied successfully to the analysis of the experimental delayed fluorescence decays measured in the range 0–250ns after X-ray pulsed irradiation of n-dodecane solutions of N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD). The modeling demonstrated that a track produced by 20-keV X-ray quanta in n-dodecane in the studied time range could be described by a set of isolated spherical spurs containing 4–5 ion pairs. The radius of such “effective” spurs were found to be about 5nm for four pairs or 9–10nm for five pairs.