Re: LNT and Collective Dose

[RuthWeiner@AOL.COM]

In a message dated 2/14/02 12:09:10 PM Mountain Standard Time, bill-field@UIOWA.EDU writes:



> Ruth, in your example below, the population is not at all defined so the concept of collective dose and collective risk can not be used.  Collective dose and collective risk can only begin to be considered valid if the exposed population can be well described and quantified


I do transportation risk assessment and have published a number of studies in this area.  The method we use may be outline (without details) as follows:

1.  There is an external (surface) dose rate associated with radioactive materials during transportation.  We usually use the maximum permissible  dose rate for the source.

2.  The exposed population is the population resident in a half-mile wideband on either side of the transportation route.

3.  We calculate the collective dose in person rem, with an expression that I won't bore you with here, but which has been extensively reviewed and verified and validated, and has been in use since about 1977.

4.  I would prefer to leave it at that, but at the insistence of our sponsors, we multiply that collective dose by 0.0005 and report potential excess latent cancer fatalities attributable to the radioactive emissions from thge material being transported.  The numbers, as you can imagine, are tiny.  We also report collective dose, by the way.


However, the only characterization of the exposed population is the old trio of time, distance from the source, and shielding.  We are not trying to determine what anybody's cancer risk is, just what the contribution of radiation from a passing vehicle might be.  That strikes me as a perfectly OK example of risk assessment, if a somewhat mindless application of the LNT (which I have argued that it is).  But in such an analysis, nothing but greater uncertainty would result if we tried to characterize the population more specifically.


If it were up to me, I'd stop with the collective dose.


Ruth Weiner, Ph. D.

ruthweiner@aol.com