Radioactive mineral

[ROBBARISH@aol.com]

Hello Radsafers:

Although I'm usually on this forum discussing in-flight radiation, I had an 
opportunity to do some work last week that directly relates to the recent 
thread on radioactive minerals.

A few weeks ago, Sotheby's (a major British-American company) held an auction 
of rare minerals. One of the items was a piece of novacekite, mined in 
Brazil.  A picture of the object can be found at:

http://www.sothebys.com/auctionhouse/sneak/_popups/ah_mineral5_1200_popup.html

I was consulted by an agent of the auction house with regard to packaging and 
shipping the item to its new owner. Because it was radioactive, the piece was 
never exhibited to the public prior to the sale. For your information, here 
is some data on this mineral:

Material: Novacekite  (Pronounced: No-va-SEE-kite)

Chemical Formula:  Mg(UO2)2(AsO4)2·12(H2O)  

Composition:  Molecular Weight = 1,058.38 gm)  
      Magnesium  (Mg) 2.30 % 
      Uranium  (U) 44.98 %   
      Arsenic  (As) 14.16 %   
      Hydrogen  (H) 2.29 %   
      Oxygen  (O) 36.28 %  

So this is one of the naturally radioactive minerals that might also be in 
the collection of the British Museum. This particular piece (don't fail to go 
look at the picture) is considered one of the finest and largest examples. It 
was sold for $125,000. I think that value makes it of "museum quality."

I'll be writing up my measurements as a note for Health Physics. I think the 
photo would be a good candidate for the cover illustration. As a quick 
summary, I estimated the object to contain about 40 uCi (1.48 MBq) of Uranium 
in equilibrium with members of its decay series. After removal of the 
particle radiation by using a single sheet of 1.6 mm Pb, a "quick" HVL 
determination for the penetrating component showed a value of about 17 mm. 
This tabletop experiment seemed to match the known HVL of radium pretty well. 
I'll be using this info for my box design. From looking at the regulations, 
it's my understanding that because this is less than 100 uCi of "source 
material" in the form of natural uranium it doesn't need to be licensed. If 
anyone on the list knows more about this than I do, and I expect many of you 
do, feel free to contact me at my personal e-mail address.
Rob Barish
robbarish@aol.com
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