Radiation Levels

[alpha_taur1]

There has been considerable discussion about radiation levels in interplanetary space and the tolerance of certain bacteria to radiation. There have been some bland statements made on certain popular science websites (that should know better) that deinococcus radiodurans can live in the core of a Nuclear Reactor. The subject of radiation is a morass of different units, such as Becquerels and Curies for activity, Rems, Rads, Grays and Sieverts for various types of dose, and ergs and electron volts for units of energy, not to mention solar flux. I'll stick to the units I know, which will probably not please everybody.<br /><br />I think we need to take stock of the facts. Radiation dose equivalent is generally measured in Sieverts. 1 Sievert is equivalent to 1 Gray for Beta and Gamma radiation. Alpha particles do about 20 times more damage than gamma rays, so 1 Gray of Alpha particle radiation is equivalent to 20 Sv.<br /><br />A fatal single dose for humans is generally quoted at around 10 Sv, or 10,000mSv, and levels of 1 Sv will cause severe but temporary radiation sickness. 5 Sv over a month is fatal to 50% of the population (LD50) <br /><br />The general population on Earth receives about 2-3mSv per year, unless they live in Ukraine or other contaminated areas. This is derived from rocks, soil and cosmic radiation.<br /><br /> Deinococcus radiodurans is extremely resistant to radiation, and will withstand total doses up to 15000 Sv, although the population starts to drop off around 6000 Sv. <br /><br />A typical nuclear reactor contains about 50-100 tonnes of Uranium which is contained within fuel rods at around 2-3%. As this decays, daughter isotopes are produced, which are even more hazardous than the Uranium 238.<br /><br />Future travellers to Mars would be subjected to about 0.3 Sieverts per year, and slightly less on the surface of Mars. That's about 100 times the dose rate of the average population on Earth. A solar particle event can increase the radiation dose by