Re: Pu Toxicity

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

>          Cancer makes Pu an even greater risk (somebody please check the > 
         following numbers):

Sure thing, my friend.  Sorry it's taken so long.

>          Deaths from 0.1 mg Pu-239 (0.0001 g) inhaled: 0.1 mg =
>          0.0001 g x 0.062 Ci/g = 6.2 E-6 Ci x 3.7 E10 Bq/Ci = 229,400
>          Bq.  The EDE for Pu-239 inhaled is ca 1 E-4 Sv/Bq so 0.1 mg
>          inhaled gives 229,400 Bq x 1 E-4 Sv/ Bq = 23 Sv or 2300 rem.

So far, so good.

>          Given that the risk of death is @ 5 E-4/rem,
>          the risk of death from 0.1 mg Pu-239 inhaled would be 2300
>          rem x 5 E-4/rem  = 1. Thats high!

That's bogus.

First of all 2300 x 5 E-4 is 1.15, greater than one.  That's a meaningless 
probability value.  What's wrong with this picture?

The linear relation (risk_per_unit)x(units) = (total risk) is only an 
approximation, the second term of a binomial expansion.  It works fine when 
the total risk is itself small (0.05 or less), but I wouldn't use it for 
general cases, any more than I'd use 1/2*m*v^2 for kinetic energy of all 
particles.  (sometimes m=0; sometimes v is close to c.)

I'll cut to the chase.  The general expression is

[1 - risk_per_unit]^(units) = [1 - total_risk].

Intuitively, [1-risk_per_unit] is one's chance of *surviving* one unit.  One 
need only *not survive* one of the (units) units (for which the total risk 
for a single unit is assumed to be known) for the bad result predicted by 
(total_risk) to ensue.  

Using Paul's numbers with my formula, I got a total_risk of 0.68 or so.

If anyone has any questions, I'll gladly walk through another example.

           Albert.


Albert Lee Vest    avest@magnus.acs.ohio-state.edu
health physicist        Office of Radiation Safety
(614)292-0122            The Ohio State University
My employer did not review or approve this message.