[ RadSafe ] Reporter's question about lower limits of detection

[Wald, Matthew]

I have been a "lurker" on this list for a couple of years, and I write intermittently about nuclear power. 
Could someone who is expert on this subject please help me with a radiation measurement question?
What is the lower limit of detection for strontium-90 in fish ?
Background: 
The Vermont Department of Health samples fish from the Connecticut River. It recently reported finding strontium-90 in some samples, slightly above what it said was the lower limit of detection, 47 pCi/kg. See: http://healthvermont.gov/enviro/rad/yankee/tritium.aspx

A website called Vermont Digger, http://vtdigger.org/2011/08/02/vermont-yankee-4/, reported on the result.  But Vermont Digger also says that New York measured 8 pCi/kg. 

http://vtdigger.org/2011/08/04/shumlin-vermont-yankee-not-necessarily-source-of-strontium-90-in-fish/

The underlying issue is whether the strontium came from the Vermont Yankee reactor, in Vernon, near the Massachusetts border, which had a leak from an underground pipe, or whether it is from fallout or some other source.  But I have another question. 
What is the lower limit of detection? 8 picocuries per kg? 47? Some other number? And what determines the lower limit? 
I would appreciate any explanation. 

Thank you. 
--- Matt Wald


Matthew L. Wald
Washington Bureau
The New York Times
1627 Eye St NW, Suite 700
Washington, DC 20006
202-862-0363
cell: 202-997-5854
fax: 202-318-0057

http://www.nytimes.com/info/nuclear-energy/
twitter: mattwaldnyt

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