[ RadSafe ] Sv (and rems) are NOT restricted to stochastic effects

Ronald Frick rfrick at gammacorp.com
Wed Nov 29 13:46:25 CST 2006

ICRP 60 states: "The equivalent dose is not always the appropriate quantity for use in relation to deterministic effects because the values of radiation weighting factors have been chosen to reflect the relative biological effectiveness (RBE) of the different types and energies of radiation in producing stochastic effects.  For radiations with a radiation weighting factor larger than 1, the values of RBE for deterministic effects are smaller than those for stochastic effects.  The use of the equivalent dose to predict deterministic effects for high LET radiations, e.g. neutrons, will thus lead to overestimates."

See also ICRP 58, "RBE for Deterministic Effects".

Ron Frick

>>> Douglas Simpkin <dsimpkin at wi.rr.com> 11/29/2006 8:21 AM >>>
Perhaps it's the neurons misfiring, but I'm confused.

In the discussion of the past couple of weeks on the Po-210 
poisoning, a number of folks have indicated that the Quality Factor 
(QF) or radiation weighting factor for alphas should not be 
considered when stating the magnitude of deterministic effects. 
Rather, they presume the QF is restricted to describing stochastic effects.

This is absolutely wrong.

The QF is based on radiobiological experiments of cell killing 
effects, and you can't get much more deterministic than that! The QF 
for alphas is 20 because the alphas dump so much more energy across 
the cell nucleus, and therefore cause that much more deterministic 
biological damage compared to sparsely ionizing x rays.

Indeed, the effective dose, or effective dose equivalent, (also 
confusingly in Sv or rem) is defined only for stochastic effects. But 
that's not the concern here.

My rough estimate of 0.12 ug = 0.53 mCi (the amount of Po-210 stated 
by that great repository of societal wisdom, Wikipedia, as lethal) 
uniformly spread through the liver yields a liver dose in the 
1000-2000 rad range, or 20,000 to 40,000 rem to the liver.

Enough to mess up anyone's day.

ps. And no, I'm not apologizing for non-SI units!

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