Re: Some questions on Pu

[JMUCKERHEIDE@delphi.com]

Following up on Dr. Cohen's note:
 
> The "one millionth of an ounce" is pure propaganda. For Pu, the important 
> risk is not ingestion, but inhalation. A toxic inhalation dose is a about 
> 200 micrograms, whereas an ingestion dose is about 1 gram. Inhalation is 
> a very difficult process to achieve--- in experiments with dogs, it took 
> a lot of technology to arrange for the dogs to inhale appreciable 
> amounts. A starting reference on these things is my paper in Health 
> Physics 32, 359-379 (1977).
>         There was a SNAP power source made of Pu-238 that burned up in 
> the atmosphere many years ago and it does contribute some to our dose 
> from Pu. I'm sure references to it can be found in UNSCEAR Reports. I 
> don't remember details, but I am sure doses are a tiny fraction of 1 
> mrem/year, and that would very probably apply to the case you asked about.

Per UNSCEAR 1993: a SNAP-9A, 1964, about 600 TBq; the ingestion dose
commitment for the temperate latitudes is 1.8 nSv, the southern hemisphere
average is 1.2 nSv, and northern hemisphere avg is 0.3 nSv (world avg 0.4 -- 
89% of population is in the north). A world population of 6 billion
(considering future growth during lifetime of Pu-238) results in an estimated
2.4 man-Sv.  The inhalation dose commit for the southern hemisphere temperate
region is 2400 nSv, 1600 nSv for avg, 400 nSv northern, 530 nSv world avg. For 
the population of 4 billion at the time of reentry, a population dose of 2100
man-Sv. 

Note that Pu-238 from atmospheric weapons testing is about half the SNAP-9A
inventory (330 TBq), but mostly in the northern hemisphere. 

Note also that the low dose effects of Pu are related also to subcutaneous
injection (not usually considered a likely environmental pathway :-)  but
don't handle Pu bare-handed with an open wound :-) 

> Bernard L. Cohen
> Physics Dept.
> University of Pittsburgh
> Pittsburgh, PA 15260
> Tel: (412)624-9245
> Fax: (412)624-9163
> e-mail: blc+@pitt.edu

Thanks.

Regards, Jim Muckerheide
jmuckerheide@delphi.com
Radiation, Science, and Health, Inc