Integral characteristics of bremsstrahlung and pair photoproduction in a   medium
  The bremsstrahlung of an electron and $e^{-}e^{+}$-pair creation by a photon in a medium is considered in high-energy region, where influence of the multiple scattering on the processes (the Landau-Pomeranchuk-Migdal (LPM) effect) becomes essential. The integral characteristics: the radiation length and the total probability of radiation and pair photoproduction are analyzed under influence of the LPM effect. 
V. N. Baier and V. M. Katkov