RE: Plutonium vs Natural Thorium

["Bradshaw, Keith" <Keith.Bradshaw@nnc.co.uk>]

> -----Original Message-----
> From:	Leo  M. Lowe [SMTP:llowe@senes.on.ca]
> Sent:	Tuesday, May 09, 2000 10:47 PM
> To:	Multiple recipients of list
> Subject:	Plutonium vs Natural Thorium
> 
> 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!
> 
> 
	OK here's a league table of radiotoxicity by ingestion on a mass
basis:

	Mass for 1 Sv

	U-232    3.8 Microgram
	Pu-238  6.7 Microgram
	Am-241  39.5 Microgram
	Ra-226  97.6 Microgram
	Pu-240   595 Microgram
	Pu-239  1.76 Milligram  (note unit change)
	Th-230  6.38 Milligram
	Th-232  1.075 Kilogram  (yes KILOGRAM)

	In practice, Pu is a mixture of 239,240, 238 and 241 isotopes, with
239 predominant.  Th-230 will probably be accompanied by Th-232 which would
act to dilute the thorium specific activity (even though it comes from the
U-238 decay chain, U containing minerals also contain some  nat-Th).  U-232
is synthetic but again there's probably a few microgram of nat-U in
everyone's daily diet which would dilute the U specific activity.  So the
element with the greatest mass-for-mass toxicity might be said to be
americium, in this way of looking at things.

	Note this is strictly for fun (!!!).  Please do not base anything on
these figures.  Also, I don't pretend to have necessarily found the most
radiotoxic-by-mass nuclide here.  I have not got time.   What you want is
high dose coefficient coupled to short half-life.

	Dose coeffs from IAEA safety series 115 Table II-VI (ingestion,
members of the public).

	Personal views only

	Regards

	keith.bradshaw@nnc.co.uk

	END












	END




**********************************************************************
NNC Limited
Booths Hall
Chelford Road
Knutsford
Cheshire
WA16 8QZ

Country of Registration: United Kingdom
Registered Number: 1120437

This email and any files transmitted with it are confidential and 
intended solely for the use of the individual or entity to whom they   
are addressed. If you have received this email in error please notify 
the NNC system manager.
**********************************************************************
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html