Respirable Particles - Pu and Cassini

["William G. Nabor" <wgnabor@uci.edu>]

Radsafers,

Marvin Goldman's comments about Pu hazards on a recent RADSAFE
posting were excellent, except for one point, which I feel is
important.  Dr. Goldman states (if I may paraphrase) that
respirable particles are less than 10 microns in size.  I would
like to point out that respirable Pu particles must be _larger_
than about 0.01 microns, as well.   The reason for this is that, in
order to be hazardous, radioactive particles which have no hazard
other than their radiation must stick to the lung's surface long
enough to decay and emit that radiation.  Particles which are too
large are cleared from the lungs (if they even get that far) by the
action of the cilia.  Particles that are too small act much as
gasses and are exhaled with the next breath (less than 10% of
spherical particles of unit density smaller than .01 microns will be
deposited in the lungs, with this fraction dropping to 0 at about
0.005 microns, and while Pu particles are not likely to be spherical at
unit density, never-the-less, there will be some minimum size for them).

     Therefore, in order to be hazardous Cassini Pu must not only
be reduced to small particles, but the particles must not be too
small either.  Surely this limits the hazard even further.
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William G. Nabor
University of California, Irvine
EH&S Office
Irvine, CA,  92697-2725
WGNABOR@UCI.EDU
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