The radiation can be emitted by a radioactive substance or generated electrically. Photons are emitted in many natural processes. Whenever EM radiation is emitted and then absorbed, heat is transferred. The flame was visibly emitted from both craters and was probably created by burning gases. The remainder is emitted as radiation, mostly in the infrared. EUV radiation can be emitted in SiO2 or Saphhire. Early asymmetries are detectable by measuring the polarization of the emitted light. Small thickness avoids the problem of self-absorption of emitted radiation. The phase and direction associated with the photon that is emitted is random. These neutrons may be emitted during either spontaneous or induced nuclear fission. Light of a characteristic frequency is thus emitted. Beta particles can therefore be emitted with any kinetic energy ranging from 0 to . When the wave was emitted, it had a wavelength . In either case, this heat is also emitted from the lamp as infrared light. Metals are usually emitted into the air as particulates as well.