Size of nanoobjects in oil and gas species and materials with positron   annihilation spectroscopy
  The analytical method to determine geometry and size of nano-scale defects in oil and gas species and materials is proposed. The modeling is carried out with the parameters of the positron spectra in the angular distribution method of positron annihilation spectroscopy, and is based on the 'free electron' approximation. From the annihilation decay kinetics, it is possible to express the trapping velocity of parapositronium in pores via intensities of the positronium components and to define the concentration and radii of pores in a porous layer. As the result, size and the concentration of micro-porous cylindrical nano-objects in the silicon samples are estimated. 
V. I. Grafutin, E. P. Prokopev, L. V. Elnikova
physics.chem-ph