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detector shielding
There are numerous papers (particularly in Nuc.Inst. and Methods) on
optimizing detector shielding. But a couple of recent personal anecdotes...
Adding excessive lead can increase the background by increasing the mass
close to the detector in which cosmic neutrons can interact. One can
clearly see increasing count rates in peaks related to this background term.
While a little liner material might be helpful a low energies it can add
peaks at higher energies due to neutron induced prompt gammas. We saw this
both with a thick copper liner and with a thin teflon liner (intended to
help with cleanliness).
What is optimum depends upon what you want to detect, and at what level.
If you want to detect natural nuclides you need to invest in a low
background detector, Doe Run lead, a thick shield, etc.
If your nuclides are not coincident with natural peaks then you money is
better spent on a high resolution detector, a standard commercial shield,
and as much efficiency as you can buy.
We had a chance to compare two such systems and the results were very interesti
ng, albeit somewhat obsoleted with newer technology.
Ref: Nuc Inst and Methods A299(1990) 425-9
A low-background gamma-ray assay laboratory for activation analysis.
R. Lindstrom et al
SLABACK@MICF.NIST.GOV
...a little risk, like a bit of spice, adds flavor to life
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