Re: Uranium Analysis

[Vincent.King@DOEGJPO.COM (Vincent King)]

     Joelle,
     
     In bioassay and environmental samples analyzed isotopically for 
     natural uranium, U-234 activity is often higher than U-238 activity, 
     even though you would expect them to be in equilibrium and to have 
     equal activities.  I have heard this attributed to higher 
     'environmental mobility' of U-234 relative to U-238, although I've 
     never seen an exact explanation of how this occurs.
     
     (As an aside, I'd be interested in such an explanation if anyone else 
     in RADSAFE can provide it or direct me to it; I vaguely seem to 
     remember it having to do with U-234 passing through a couple of 
     different chemical species, namely thorium and protactinium, following 
     the decay of U-238.)
     
     On the other hand, when you chemically determine uranium content 
     (mass), you're looking at U-238 almost exclusively, since it comprises 
     almost the entire mass of natural uranium (very long half-life = very 
     low specific activity, or conversely, very high mass per unit 
     activity). 
     
     So if the final answer from your alpha spec determination incorporates 
     results from U-234 and assumes it is in equilibrium with U-238, this 
     could partially explain the higher than expected result.
     
     I don't know if this would apply to whatever you're sampling, but it 
     might be worth checking.
     
     Vincent King, CHP
     vincen.king@doegjpo.com 
     


______________________________ Reply Separator _________________________________
Subject: Uranium Analysis
Author:  Joelle Key <jkey@mail.state.tn.us> at Internet
Date:    7/20/98 09:15


Dear Radsafers:
     
I was recently reviewing a licensee request that delt with Uranium.  In the 
original request, the U content was determined chemically.  We asked
them to take more samples, and these were analyzed with alpha spec. 
The second samples showed about twice as much Uranium than the first
samples.  I called the company to ask them if they had any theories as to 
why this was so.  They said that they had the same question and asked 
their HP consultant.  The consultant told them that it was because of the 
different type of analysis.  The HP said he trusted the alpha spec more 
but that this may just be his HP bias.
     
What do you people out in HP land know about this?  Is there a reason to 
think that one analysis is more reliable than the other?  Has anyone 
studied this question?
     
I appreciate any help ya'll can give me.
     
Joelle Key
TN-DRH
jkey@mail.state.tn.us