RE: Chemical state of Ir-192 sources

[Tom Morgan <tmorgan@ISOTOPEPRODUCTS.COM>]

Ir-192 seeds are very small, typically 2 to 4 mm in length and less than one

mm in diameter.  Iridium melts above 2400 F and platinum above 1700 F.



Ir-192 is most frequently shipped in one of two source strength ranges -

10-12 Ci for high dose rate afterloaders or industrial radiography units and

0.3 to 0.7 mCi seeds encased in plastic ribbons for interstitial implants.

In either case the sources are packaged in a lead pig and placed in an outer

DOT Type A shipping container (typically a five gallon metal bucket).  



Bulk quantities of Ir-192 (hundreds or thousands of curies) are shipped less

frequently, but the principal is the same - an inner lead shield and an

outer Type B container. 



Assume a terrorist does not have access to the inner contents of these

packages.  In this case his/her only option is to place an explosive charge

on the outside surface of the package.  Exploding a few pounds of C4 would

certainly rupture the package and undoubtedly the lead pig as well.

However, the explosive force would probably not be sufficient to vaporize

the iridium pellets.  Under this scenario, the mostly like problem would be

wide spread dispersal of intact pellets and the accompanying external

radiation hazard, not inhalation of iridium oxide.



The only plausible scenario for dispersal of oxidized iridium would be if

the terrorist deliberately designed the package with the explosive in direct

contact with the seeds.  However, even this is suspect since iridium and

platinum have such high melting points.



"My opinion.  Not yours, nor theirs."



Thomas L. Morgan, PhD 



-----Original Message-----

From: Carol S. Marcus [mailto:csmarcus@ucla.edu] 

Sent: Friday, September 06, 2002 3:14 PM

To: radsafe@list.vanderbilt.edu

Subject: Chemical state of Ir-192 sources



Dear Radsafers:



I am interested in knowing the chemical state of Ir-192 in sealed sources, 

and any thoughts on what would happen chemically to the Ir-192 if it was 

exploded as a radiologic dispersion device.  I am trying to estimate 

biodistribution and kinetics if such Ir-192 were to be inhaled, ingested, 

or introduced traumatically (e.g. contaminated shrapnel).  Anyone having 

any information on biodistribution and kinetics is requested to share it 

with me.



The California Statewide Medical and Health Disaster Exercise on Nov 14th 

includes an Ir-192 RDD scenario, and I have been asked to critique our 

Exercise Guidebook.  Ir-192 in an RDD is a reasonable scenario, and I need 

to know this anyway.



If, for example, the Ir-192 is chemically just solid metal, and some of it 

is converted to insoluble oxide in the explosion, then we would worry about 

pulmonary and pulmonary lymph node deposition.  Little would ionize and get 

into the blood and other organs.  Ingested Ir-192 would just pass 

through.  If, on the other hand, much of it were to be in a soluble form, 

the biodistribution and kinetics would be entirely different.



Many thanks for any help you can give me.



Ciao, Carol



Carol S. Marcus, Ph.D., M.D.

<csmarcus@ucla.edu>



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