Variation of radiation length due to LPM effect
  The photon emission intensity spectrum is calculated taking into account influence of multiple scattering (the LPM effect) under conditions of recent CERN SPS experiment. It is shown that the theory quite satisfactory describes data. The integral characteristics: the radiation length and total probability of photon emission are analyzed under influence of the LPM effect, and the asymptotic expansions of these characteristics are derived. 
V. N. Baier and V. M. Katkov