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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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