Specimen heating The fraction of the energy in the incident electron beam which reappears in the form of X-rays, light, etc. is small, most being converted into heat in the target. The temperature rise AT is expressed as AT 4.8Egl/(kd) Eo is the incident electron energy (keV), /the current (A), k the thermal conductivity (Wcm K1), and d the beam diameter (m). Metals: k 1-4, AT is negligible. Mica: k 6x103, Eo 20 keV, /-10 nA, d= 1 m, T-160K