Re: Respirable Particles - Pu and Cassini

[Wes Van Pelt <VanPeltW@IDT.NET>]

William G. Nabor wrote:
> 
> 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).
> 
snip

Willian and Radsafers,

I always thought that for very small particles, e.g. less than 0.01
micrometers diameter, Brownian motion would cause the deposition in the
lungs to increase due to random motion contact of the particle with the
walls of the small airways.

Wes

-- 
Wesley R. Van Pelt, Ph.D., CIH, CHP                KF2LG
President, Van Pelt Associates, Inc.     
Consulting in radiological health and safety.
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