My strongest area of expertise is in the area of nuclear detectors.
Before turning to teaching, I built and used various types of detectors
as my main job for several years. I still work with detectors, but
teaching is now my primary job.
Anyway, I would be glad to help answer some questions in this thread,
but I can't tell what the question is or what the questions are.
I've read messages about survey meters scaled with different units;
about detectors employing Geiger-Meuller tubes, perhaps with thin
windows, perhaps not; messages mentioning NaI detectors; messages
mentioning, plastic scintillators; scalers; pulse-height discriminators;
etc.
These detectors and supporting electronics are used in very different
ways for very different purposes. It does not really make sense to be
discussing them in the same thread, unless someone is trying to
understand what detection methods exist and what each type is used for.
What is the point of this thread? What type of radiation are we trying
to detect, and why?
For example, if you are trying to detect daughters of radon gas that
might be electrostatically collected on a TV or computer-monitor screen,
then you probably want to detect the gamma radiation from 214-Pb and
214-Bi which are daughters of radon. The preferred way to detect these
is a NaI scintillator, ideally analyzed with a pulse-height-analysis
system (PHA) so you can confirm the gamma energies of 242 keV, 295, 353
from 241-Pb and 609 keV, 768, and 1120 from 214-Bi. If you assume these
are what you have, then you wouldn't really need to do energy analysis,
just measure the raw count rate.
If you have sufficient activity you could use a GM-tube survey meter,
but GM-tubes don't have a high efficiency for detecting gamma radiation.
To measure the gammas you would hope to have a fair amount of radon in
the room to deposit lots of daughter activity on the screen... Except
you don't really want a fair amount of radon because that wouldn't be
healthy to breathe. If the GM-tube has a thin window, you could pick up
some of the betas from 214-Pb, 214-Bi. You could also pick up alphas
from 222-Ra and 218-Po and 214-Po as long as you hold the wipe very
close to the window.
Thus, you could detect all three types (alpha, beta, gamma) from 222-Rn
and daughters stuck on a CRT screen if you have a NaI detector for the
gammas, or a thin-window GM-tube for the alphas and betas. You hope you
don't measure much from a thick-window GM-tube designed to detect gammas
(and not alpha or beta) because that would imply a high level of radon.
Plastic scintillators are best at detecting fairly high-energy beta
radiation. Their use for alpha is zilch and not much better than zilch
for gammas. A plastic scintillator would be of little value for
detecting radon daughters.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu