[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Welcome to California
Yes, I was being sarcastic to some extent and have enjoyed the clever
responses. I am aware of using very thin detectors and the use of
discrimination to reduce the signal/background ratio. I intuitively knew
that state-of-the-art field detection instruments could not distinguish
contamination at the 1 in 1,000,000 risk level. Thanks to some rough
calculations by Jerry Cohen, we can see it is indeed impossible to detect
0.8 microrem in a 20 microrem field. This is further complicated by the 20
microrem background varying by plus or minus 5 microrem through out the day.
What was not intuitively obvious to me at the time I posted here was that
state-of-the-art laboratory detection equipment could not detect most of the
commonly encountered radiological contamination at the 1 in 1,000,000 risk
level either. Not with an acceptable certainty anyway. In fact, laboratory
detection of many radionuclides is difficult at risk levels in the 1 in
10,000 to 1 in 1,000,000 range. I suppose that is why the DOE and NRC
standards are based on lifetime risk that range from 2 in 1,000 to 3 in
10,000. These risk levels produce clean-up standard we can actually detect
in the lab and sometimes the field. An interesting perspective I have found
was that the EPA's cancer risk from background radiation is (theoretically)
1 in 100.
Someone shared a Website that addresses these proposed bills and the
irrational consequences of the proposed legislation. It is:
http://www.philrutherford.com/2002_Legislation.html
Carl Speer
Real-Time Radiological Services, Inc.
www.realtimerad.com
-----Original Message-----
From: Redmond, Randy (RXQ) <RXQ@Y12.doe.gov>
To: radsafe@list.vanderbilt.edu <radsafe@list.vanderbilt.edu>
Date: Monday, June 03, 2002 4:20 AM
Subject: RE: Welcome to California
>Folks - the man is being sarcastic.
>
>> -----Original Message-----
>> From: Wes Van Pelt [SMTP:wesvanpelt@ATT.NET]
>> Sent: Saturday, June 01, 2002 6:49 PM
>> To: Speercl; BLHamrick@AOL.COM; radsafe@list.vanderbilt.edu
>> Subject: RE: Welcome to California
>>
>> Carl,
>>
>> The first thing to do is state in detail the question you wish to answer
>> by doing a gamma scan over a large area. By your last sentence, it
appears
>> you want to measure the extent of residual contamination that produces a
>> cancer risk of 1 in 1,000,000. This requires dose modeling, including
>> ingestion of vegetables grown on the land, drinking water from wells,
>> drinking cow's milk, breathing airborne dust, as well as direct gamma
>> exposure. But this is quite easy using commonly available environmental
>> dose codes.
>>
>> Then just equate radiation dose to cancer risk using the Linear
>> Non-Threshold theory. (Please, no flames.)
>>
>> The big problem, as I see it, is determining the depth over which the
>> residual contamination is spread. For example, does it go down 4 inches
>> of 4 feet? And how is it distributed by depth? The only way I know to
>> determine this is to drill holes and analyze the core samples for
>> radionuclide concentration and also doing down-hole gamma readings. This
>> gets expensive and requires a lot of drill holes.
>>
>> Regards,
>> Wes
>>
>> Wesley R. Van Pelt, PhD, CIH, CHP
>> Wesley R. Van Pelt Associates, Inc.
>> Consulting in Radiation Safety and Environmental Radioactivity.
>> <http://home.att.net/~wesvanpelt/Radiation.html>
>> <mailto:wesvanpelt@att.net>
>>
>> -----Original Message-----
>> From: owner-radsafe@list.vanderbilt.edu
>> [mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Speercl
>> Sent: Friday, May 31, 2002 10:36 PM
>> To: BLHamrick@AOL.COM; radsafe@list.vanderbilt.edu
>> Subject: Re: Welcome to California
>>
>> I am in the beginning stages of starting my own business of performing
>> radiation scanning surveys of large land areas. If I was to perform
gamma
>> surveys for license termination in California, what would be the "best"
>> technology available to perform these surveys? I know sampling will have
>> to be done and can be counted on a HPGe, REGe or the like, but what about
>> land area scanning? Typically in the past 2 x 2 NaI detectors were used,
>> and large area plastic scintillator (LAPS) detectors are comparable, but
>> the "Best" is . . . .? I have thought about getting a 4 x 4 x 4 NaI but
>> then a 4 x 4 x 16 NaI would be better. . .then four 4x4x16 NaI detectors
>> would be better still. But then this large of a detector array would
mean
>> I would be averaging a point source over the field of view of the
detector
>> system . . . I run into the same line of thinking when I try to figure
out
>> how fast to scan. I typically take a moving one second count with a LAPS
>> using a GPS, but wouldn't a one minute static count be better before
>> moving on? What detector and scanning method is out there that can
>> measure gamma emitting radioisotopes to a 1 in a 1,000,000 cancer risk?
>>
>>
>> Carl Speer
>> Real-time Radiological Services, Inc
>> Las Vegas, NV
>> 702-639-0066
>> www.realtimerad.com <http://www.realtimerad.com>
>>
>************************************************************************
>You are currently subscribed to the Radsafe mailing list. To unsubscribe,
>send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe
>radsafe" (no quote marks) in the body of the e-mail, with no subject line.
>You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/
>
************************************************************************
You are currently subscribed to the Radsafe mailing list. To unsubscribe,
send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe
radsafe" (no quote marks) in the body of the e-mail, with no subject line.
You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/