4.4.3.1 The Role of Radiation

At the temperatures achievable in the fission core of the primary (up to 10^8 degrees K) nearly all of the energy is present as a thermal radiation field (up to 95%) with average photon energies around 10 KeV (moderately energetic X-rays). Most of this thermal energy is rapidly radiated away from the surface of the "X-ray fireball", composed of the expanding X-ray opaque material of the core and tamper. It is this powerful flux of energy in the form of X-rays that is harnessed to compress the fusion fuel.