Sv = Sievert a unit of effective total dose (An actual dose, measured in Grays, multiplied by the RBE (Relative Biological Effectiveness)
1 Gray is 1 Joule of energy absorbed per kilogram = 100 Rad (Rad = Radiation absorbed dose).
1 Sv is equivalent to 1 REM (Roentgen Equivalent Mammal/Man) A Roentgen (pronounced Rent gen (hard g)) is the amount of radiation that produces a certain amount of ionization. It is nominally referring to reasonably hard X-rays (say, 60 kV on up). The REM is a way to account for the fact that certain particles might have the same "ionizing power", but have very different biological effects. The idea behind the REM is that, roughly, the same effects (i.e. damage) would occur from 1 REM of whatever sort of radiation, even though the effects from 1 Rad of Xrays might be very different from 1 Rad of 100 keV protons or neutrons (for instance). Roughly is the operative word here..... Radiation metrology (particularly at low fluxes and doses) is tricky, and assessing biological effects is even more flaky.
The RBE depends on the kind of particle (fast neuts are an RBE of 10)
Just for giving you an idea... 450 microGrays/yr is a typical cosmic ray dose.
5-6 Sieverts is usually a lethal dose (comparable to the dose received by the poor devils a couple of years ago in Japan who were mixing fissionable material in a bucket on the floor and had a little "criticality problem")
Created on Wednesday, March 14, 2001 6:09 PM EDT by James Lux