Background radiation equivalent time BRET value corresponding to a dose of radiation is the number of days of average background dose it is equivalent to. It is calculated from the equivalent dose in sieverts by dividing by the average annual background radiation dose in Sv, and multiplying by 365: The definition of the BRET unit is apparently unstandardized, and depends on what value is used for the average annual background radiation dose, which varies greatly across time and location. The 2000 UNSCEAR estimate for worldwide average natural background radiation dose is 2.4 mSv (240 mrem), with a range from 1 to 13 mSv. A
Electromagnetic radiation (or "extreme") ultraviolet. UV, with X-ray and gamma radiation, are referred to as ionizing radiation due to the ability of photons of this radiation to produce ions and free radicals in materials (including living tissue). Since such radiation can severely damage life at energy levels that produce little heating, it is considered far more dangerous (in terms of damage-produced per unit of energy, or power) than the rest of the electromagnetic spectrum. The heat ray is an application of EMR that makes use of microwave frequencies to create an unpleasant heating effect in the upper layer of the skin. A