[ RadSafe ] Re: radioactive contamination of silver

Wed Mar 30 20:23:02 CEST 2005

Franz,

I actually got so wrapped up in the processes involved that I forgot the original question was about Po-210 and neglected to mention it specifically; I got hung up on PO-214 and 218.  But the same process is employed.  Heating the silver past 1140C will boil off the Ra-226, Rn-222, Po-218, and Po-214.  The Pb-210 will remain (BP 1755C), and the Po-214 and Po-210 will grow back in almost immediately.  With a 138-day T-1/2 it will take a while before we start to detect the presence of Po-210 due to alpha decay (1 uCi of Pb-210 produces 2.2 E6 atoms of Po-210 produced every minute).  Heating the mixture past 1755C will also remove the Pb-210 (also Bi-214 and Bi-210).  After that, it will take a LONG time for those radionuclides to grow back in, because we have to wait for daughters of Ra-226 (1600 year T 1/2) to be produced from Th-230.

These are all generalities.  Just like heatng a pot of water to 100C does not cause all the water to immediately flash to steam, so also heating a mixture of metals will not cause all the lead, etc. to immediately volatize and go away.   

Yeah, it's an interesting problem, and certainly one which cannot be adequately discussed in a few sentences.  There are also ramifications far beyond the effect on Kodak's film quality.  Right now I've got to get back to work.....

Glenn Marshall

-----Original Message-----
From: Franz Schönhofer [mailto:franz.schoenhofer at chello.at] 
Sent: Tuesday, March 29, 2005 5:28 PM
To: Glenn R. Marshall; sontermj at tpg.com.au; radsafe at radlab.nl
Subject: AW: [ RadSafe ] Re: radioactive contamination of silver

Glenn, Mark,

Thank you for your very interesting postings. In the meantime I had an excellent explanation from Mark, which is very reasonable and btw shows him as a real expert on this case. It is past midnight in Austria and tomorrow morning I will go to Rome for a week, I still have to sort my overheads and pack my luggage, so I would like to answer your message and Marks in detail after my return. One quick comment: Po-210 (T 1/2 165 days) is a daughter of Pb-210 which has a half-life of about 22 years. So decay of Ra-226 will no quickly replace the removed Po-210, even if Pb-210 would not be removed by heating - which I doubt. 

Yes, it is a tricky and difficult question. I enjoy this kind of scientific discussion much more over others recently on RADSAFE.

Franz Schoenhofer
PhD, MR iR
Habicherg. 31/7
A-1160 Vienna
AUSTRIA
phone -43-0699-1168-1319

> -----Ursprüngliche Nachricht-----
> Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im 
> Auftrag von Glenn R. Marshall
> Gesendet: Montag, 28. März 2005 15:55
> An: Franz Schönhofer; sontermj at tpg.com.au; radsafe at radlab.nl
> Betreff: RE: [ RadSafe ] Re: radioactive contamination of silver
> 
> The melting point of silver is 962C.  The Boiling Point of uranium is 
> 3818C; BP of thorium is 4790C; BP of radium is 1140C; BP of polonium
is
> 962C; BP of lead is 1755C.  So it seems that merely melting the silver 
> will remove only Po from the mix, which is quickly replaced by decay
of
> radium.  Heating the ore to a temperatuure greater than 1140C (but
less
> than the BP of silver - 2212C) would boil off the radium and other
short-
> lived progeny but not the silver.  Does this make sense?
> 
> Glenn
> 
> -----Original Message-----
> From: Franz Schönhofer [mailto:franz.schoenhofer at chello.at]
> Sent: Friday, March 25, 2005 5:08 PM
> To: sontermj at tpg.com.au; radsafe at radlab.nl
> Subject: AW: [ RadSafe ] Re: radioactive contamination of silver
> 
> 
> Mark and RADSAFErs,
> 
> That Po-210 must be present in ores of Cu-U-Au-Ag mining is not 
> surprising. That the various procedures of refining of gold, silver
and
> electrolytic refinement of copper which involves several meltings and 
> electrotechnical processes would not remove Po-210 is more than 
> surprising. A very common method to separate and determine Po-210 is
based
> on the volatilisation of Po-210. Therefore I draw the conclusion that 
> traditional methods for silver production should simply by the fact of 
> melting remove any contamination attributable to Po-210.
> 
> I am of course open to any explanation showing that this is not the
case.
> 
> Franz
> 
> Franz Schoenhofer
> PhD, MR iR
> Habicherg. 31/7
> A-1160 Vienna
> AUSTRIA
> phone -43-0699-1168-1319
> 
> 
> > -----Ursprüngliche Nachricht-----
> > Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im 
> > Auftrag von sontermj at tpg.com.au
> > Gesendet: Freitag, 25. März 2005 11:51
> > An: radsafe at radlab.nl
> > Betreff: [ RadSafe ] Re: radioactive contamination of silver
> >
> > Regarding the thread on contamination of silver:
> >
> > Can I suggest that an often-unrecognised pathway for silver to get 
> > contaminated with radionuclides is from usually-tiny amounts of NORM 
> > in the silver ore that can carry over
> into
> > the final refinery process.  At a Copper-Uranium-Gold-Silver mining 
> > and processing facility where I
was
> once
> > the RSO, we had to hold
> > back the initial silver shipments because we had found unexpected
> Po-210
> > contamination in it (and Kodak
> > didnt want it!).  We made adjustments to the metallurgical process
to
> > reduce this carry over.
> >
> > Mark Sonter
> > _______________________________________________
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