This reminds me a thread we had two years ago. If you were not a phys-L-er
at that time try the following. Go to a screen of your TV (after it was on
for an hour or so, or to your computer screen, and wipe its dirt with a wet
tissue paper. Then put the dirt in front of your GM tube and count for
about 5 minutes. Most likely you will observe at least two or three times
more counts than without the tissue. The dominant half-life, if I recall
correctly was something like 40 minutes. Then a tail with T=10 hrs or so.
I attach below a copy of my posting of two years ago which addressed this
issue for the benefit of anyone still interested in this topic (or new to
this list) :
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Date: Wed, 10 May 1995 23:07:34 -0500
From: Thomas Walkiewicz <WALKIEWICZ@EDINBORO.EDU>
Subject: Radioactive Balloon
I have a paper scheduled to appear in The Physics Teacher (possibly September)
which may be of interest to the group. The basic idea is to inflate a balloon,
rub it with fur to build up a static charge, and leave it suspended in air for
about 45 minutes (comparable to the effective/compound half life of Rn-222
decay products). Deflate and squeeze as much of the balloon as close as
possible to a Geiger tube and count. My record so far is 11,660 counts per
5 minutes above background (BG was 150 counts per 5 min)!
The TV/monitor screen wipe is "old" news (I was told of this in the late 60's)
but it is very interesting each time it is rediscovered. This is also directly
connected to my paper - Radioactiveball in TPT, Vol. 30, pp. 16-17, Jan 1992 -
in which I, too, probably rediscovered how a handball or racquetball picks up
enough radon decay products to enable a decay study to be made with a G-M tube.
(Also, see my letter to the editor - Radioactivity as a Function of Speed in
TPT, Vol. 31, p. 260, May 1993 - for an interesting twist.)
It turns out that any negative-charged object (this statement can be subject
to investigation) can pick up enough radon decay products to be counted. A
gamma-ray spectrum (NaI or GeLi) provides exact identification of these
products and you can even follow the half life of an individual gamma (alpha
spectra accomplish similar goals).
Although the balloon result can be spectacular, the standard method to extract
a radioactive dirt sample from the atmosphere by filtering air thru, eg., a
ShopVac (I use 8 layers of lens cleaner tissue because it is available to me),
can be more reliable and provides a much higher activity. (See AJP, Vol. 30,
pp. 120-124, Feb 1962; AJP, Vol. 41, pp. 921-922, July 1973; and AAPT Announcer
Vol 7, p. 64 (4) 1975.)
Keep in mind that thoron (Rn-220 from the thorium series) decay products
deposited or filtered are governed by 10.64 h Pb-212 and the subsequent 60.55
m Bi-212 activities. This means that an initially clean screen left for 1-2
hours before wiping will show mainly the activities of radon daughters, while
a screen left on overnight will have become saturated with this radon activity
and will only continue to build up the longer activities of thoron daughters.
This can be a complicating feature in simple decay measurements.
My RECORD of 11,660 cp5min was achieved in a room where I measured the radon
concentration to be only 0.3 pCi/l, comparable to the average U.S. outdoor
concentration. See details in my forthcoming TPT paper.
PROPOSAL: Please help me accumulate data by posting or e-mail to me directly
(Walkiewicz@Edinboro.EDU) your results and method for highest net activity
measured in 5 minutes via techniques described above (filtered dirt over 24 h
can become very hot). I will post a summary of this info. Include any useful
details, such as measured radon levels. Try a variety of locations, especially
basement areas having exposed soil.
Thanks for your cooperation
***************
It seems that this balloon idea is still of interest according to a recently
published paper, "Radioactive balloons: experiments on radon concentration in
schools or homes" in a recent issue of Physics Education, pp.97-100. These
authors quote an initial activity of 7644 counts per minute in the basement
of a building where the radon concentraction was found to be 0.8 pCi/l.
Is this a record via my above challenge or can anyone do better?