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[Phys-L] Re: Survey Meters



This means the data represent either the gammas or the betas (usually
gammas) from 214-Pb and 214-Bi, which, as I mentioned, are typically
what one examines when trying to detect radon.

Radon does indeed have a half-life of 3.8 days. If it's present at a
steady rate in the room, and assuming the CRT display is always on, then
an equilibrium ratio of radon daughters exists on the screen. The radon
itself, being a gas, is not efficiently trapped on the screen. The
trapped daughters are 218-Po (3.05 min (alpha)), 214-Pb (26.8 min
(beta-gamma)), 214-Bi (19.9 min (beta-gamma)), 214-Po (0.16 ms (alpha)),
210-Pb (22.3 years (beta-gamma)) [and we can stop there for this
discussion even though there are more daughters before we hit
stability].

So... You take a wipe from the screen and you get 218-Po, 214-Pb,
214-Bi, 214-Po, and 210-Pb... And you get little else unless the CRT has
been there long enough (tens of years) for appreciable 210-Pb to decay.
Particularly, you don't get 222-Rn. You also won't see much 218-Po and
214-Po because you have to be looking for alphas, plus their equilibrium
values are low due to their shorter half-lives.

The gamma emitters are the 214-Pb and 214-Bi, with half-life of 26.8
minutes followed by half-life of 19.9 minutes. Hence the decay curve is
really a compound curve, but with poor statistics it looks like a simple
decay curve with half-life near 40 minutes.

There is very good reason why most radon detectors are looking for
gammas from 214-Pb and 214-Bi. That's the easiest way to know there is
radon around.


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu


The half life of radon is 3.8 days, and this half life
is about 40 minutes.....
Is this the radium a, b ,c, c', d route?


Brian Whatcott Altus OK Eureka!