where formula_1 is the radiation length of the matter, and formula_6 is the critical energy (the critical energy can be defined as the energy in which the bremsstrahlung and ionization rates are equal. A rough estimate is formula_7). The shower depth increases logarithmically with the energy, while the lateral spread of the shower is mainly due to the multiple scattering of the electrons. Up to the shower maximum the shower is contained in a cylinder with radius < 1 radiation length. Beyond that point electrons are increasingly affected by multiple scattering, and the lateral size scales with the Molière radius formula_8. The propagation of the photons in the shower causes deviations from Molière radius scaling. However, roughly 95% of the shower are contained laterally in a cylinder with radius formula_9.