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Carl,
Now let's see. Assuming a risk of 2E-4
/rem of exposure, the 1E-6 risk limit might correspond to an
lifetime dose of ~5.0 rem. Assuming an average 70 yr lifetime,
this corresponds to a steady state doserate of ~8E-4 mrem/hr. Given typical background levels of ~2E-2 mrem/hr, it
would appear that the signal to noise ratio might pose a enormous problem ,
especially when as Tom suggests, you wouldn't even know what "signal" to look
for. So it seems that it regardless of what instrument is used-- the technical
problems could be insurmountable
But don't be discouraged. I have an
approach that just might work. Perhaps you have noted the string on "sensory
perception of radiation" on this website. I may possibly have the capability to
"perceive" very low levels of radiation. The method I use is Intuitive Radiation
Sensing (IRS). Although the IRS method has not been scientifically validated,
you need to remember that we are dealing with the state of California where
science is unimportant, as evidenced by the recent legislation. All
you would need is a few slick lobbyists to sell the IRS method to state
officials. Of course my services would not be cheap, but then
politicians have been known to squander money on sillier
things.
Jerry
----- Original Message -----
Sent: Saturday, June 01, 2002 12:42
PM
Subject: RE: Welcome to California
It's worth noting that bigger is not always
better---you always need to have some idea what contaminants you are looking
for. For example you want to use a fairly thin NaI(Tl) crystal when
looking for lower energy photon emitters (e.g., 60 keV from Am-241)...the
thicker detectors result in lower signal to noise
(higher relative background), which in affects the detector's
sensitivity. Its an optimization problem. There is no ONE right
detector that fits every situation.
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
-----Snip-----
SB 1444, the worst of the quartet before the legislature sets a
simple, and simple-minded standard, of ZERO radioactivity above background
for unrestricted release, using the BEST available technology, and
prohibiting any averaging of activity over any "larger area" of potential
contamination.
Snip
Barbara L. Hamrick
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