Caveman NORM doses

[rick_strickert@pc.radian.com]

A Radsafer earlier noted:

>   Remember, the human experience is that the background dose rate has
>   been decreasing for as long as humans have been a species. The dose
>   rates millions of years ago were significantly higher than they are now
>   because, in millions of years, at least some of the natually occurring
>   radioactive material existing then has decayed to what we see now.

The long U-238 and Th-232 half-lives limit the equilibrium rates of their
respective decay products.  Going back 10 million years (well before any
humans existed) would increase the NORM decay rates (and thus the doses) by
less than 1 percent, even considering the increased U-235 fraction.  Unless
exposure through NORM inhalation/ingestion/direct pathways was drastically
different for the working-class caveman, NORM doses were probably
comparable to NORM doses today.

Based on studies of cosmic ray spallation products, the cosmic ray flux in
our solar system has been relatively constant over the past billion years.

Rick

Richard G. Strickert, Ph.D           |  "Errors using inadequate data
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