[ RadSafe ] Reporter's question about lower limits of detection
Dixon, John E. (CDC/ONDIEH/NCEH)
gyf7 at cdc.gov
Tue Aug 9 14:57:27 CDT 2011
I recommend you consult instrumentation/radiation physics texts written by James Turner and Glenn Knoll. Once you digest that material for a few months, then you might understand the question you are asking. Lower limits of detection depend upon the physics of the detection media and the conditions under which it is used.
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Wald, Matthew
Sent: Friday, August 05, 2011 11:31 AM
To: 'radsafe at agni.phys.iit.edu'
Subject: [ RadSafe ] Reporter's question about lower limits of detection
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 ?
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.
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.
--- Matt Wald
Matthew L. Wald
The New York Times
1627 Eye St NW, Suite 700
Washington, DC 20006
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