Plutonium vs Natural Thorium

["Leo M. Lowe" <llowe@senes.on.ca>]

Previous posts have noted that:

1) natural thorium (Th-232) has a lower ingestion ALI than Pu-238 or Pu-239, 
   but also 
2) one would have to inhale 10 grams of thorium vs only 28 micrograms of
Pu-239    to get 1 Sv.

Would not a better comparison be to natural Th-230 in the U-238 series?
The ICRP inhalation dose conversion factor for Th-230 is almost the same as
that for Pu-239 i.e. 1.4E-05 Sv/Bq versus 1.6E-05 for Pu-239 (inhalation
class S).  Also, the specific activity of Th-230 (77 000 y) in only about a
factor of three smaller than that of Pu-239 (24 100 y).

On this basis, one would need to inhale about 100 ug of Th-230 to get 1 Sv.
 This type of calculation could be extended to Ra-226 which is even more
"toxic" (on a per gram basis) than Pu-239.

Just think, all this radioactivity is in our own backyards!



Leo M. Lowe, Ph.D.
Principal, Senior Health and
Environmental Physicist

SENES Consultants Limited
121 Granton Drive, Unit 12
RICHMOND HILL, Ontario
Canada L4B 3N4
Tel:  (905) 764-9380
Fax:  (905) 764-9386
Email Address:  llowe@senes.on.ca
Web Site:  http://www.senes.on.ca/(under renovation)
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