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Re: rem vs. rad

I think we're asking the wrong question.  Instead of basing the cutoff on
dose, base it on effect.  Use rem for ANY dose when estimating stochastic
risks.  Even if the dose is high, if I want a stochastic risk estimate, I
have to use rem (would you try to estimate cancer risk using rads?).  As
Bob Flood pointed out, the whole stochastic risk model - complete with
radiation weighting factors (ie.Q) was "founded" on high doses, and if I'm
estimating risk for a stochastic effect, by definition I have to use rem.
For non-stochastic effects, one should use rad to determine, for instance
if the dose is above the threshold for some particular effect.  
Example:  I rapidly get 400 rem uniform whole body dose (just to make it
interesting, it's from neutrons with Q=2, so absorbed dose is 200 rad).  To
estimate my cancer risk, I use rem.  To evaluate the potential for and
severity of a non-stochastic effect, I use rad.

Keith Welch
Thomas Jefferson National Accelerator Facility
Newport News VA
Ph: (757)269-7212