No subject
Sun Mar 6 13:40:07 CET 2011
anything with that... you have already taken a lethal dose of radiation.<br=
><br><div class=3D"gmail_quote">On Tue, Mar 15, 2011 at 11:31 PM, john arcl=
ight <span dir=3D"ltr"><<a href=3D"mailto:arclight at gmail.com">arclight at g=
mail.com</a>></span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin: 0pt 0pt 0pt 0.8ex; borde=
r-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">I have actually h=
ad some training on =A0this topic, and have a pretty<br>
good knowledge of radiation instruments.<br>
<br>
What your friend needs is a low-range instrument, i.e. something<br>
capable of detecting at least beta/gamma radiation from background up<br>
to 100mRem/hr or so. The big, yellow civil defense units like the<br>
CDV-715 are high-range detectors that will only register on very high<br>
levels of radiation, such as the fallout from an actual nuclear<br>
detonation.<br>
<br>
Unless they are working around that nuclear plant, the worry is not<br>
direct exposure to radiation, but contamination from particles of<br>
radioactive material. =A0Short-term exposure to high levels of radiation<br=
>
can cause burns and sickness, and long-term exposure (such as from<br>
eating contaminated food or breathing in radioactive vapors from a<br>
steam explosion) can increase cancer risks or damage certain organs,<br>
such as the thyroid.<br>
<br>
Ionizing radiation comes in three major forms: gamma rays (high-energy<br>
photons), beta (high energy electrons), and alpha (heavy particles<br>
with two protons and two neutrons). =A0 Microwaves, radio-frequency<br>
energy and EMI from power lines are not considered ionizing radiation<br>
and not hazardous in the same way.<br>
<br>
Radiation exposure can be limited in 3 ways: time (minimize the time<br>
you are outside, for instance), distance (evacuate the immediate area)<br>
and shielding (stay inside, put stuff between you and the source of<br>
radiation). =A0Gamma rays require mass to stop. Beta rays can be stopped<br=
>
by thin metal, and alpha particles are actually stopped by the first<br>
few layers of your skin. None of these types of radiation will make<br>
you or anything else radioactive, but you can be harmed if you absorb<br>
them into your body and they continue to decay and release radiation<br>
at zero distance and with nothing shielding you from them,<br>
<br>
The type of radiation that turns normal matter into radioactive<br>
isotopes is only found inside the reactor while it's running (neutron<b=
r>
radiation) or in a particle accelerator.<br>
<br>
There are several ways to detect low levels of radiation as you might<br>
find in downwind contamination from the plant. One would be the<br>
already-mentioned Geiger-Mueller =A0counter. =A0It needs a factory-made<br>
tube with an electrode and a special quench gas sealed inside, =A0along<br>
with a 500-750VDC power supply. When a ray or particle of ionizing<br>
radiation passes through the tube and intercepts a molecule of the<br>
gas, it will ionize it and cause a spark to jump from the electrode<br>
inside to the grounded outside, registering a "click" or count.<b=
r>
<br>
All of these tubes will detect Beta and Gamma rays, and some with a<br>
thin mica window (called a "pancake" or "end window" tu=
be) will also<br>
detect alpha particles . A pancake G-M counter would be the gold<br>
standard to acquire.<br>
<br>
A serviceable alternative to the G-M tube is the ion chamber. This<br>
uses a sealed container full of gas, but it operates at a much lower<br>
voltage and the gas can be air. It operates on the principle that the<br>
air inside will become more conductive and pass more current if there<br>
is ionizing radiation passing through it. =A0You can in fact make one<br>
out of a soda can and some amplifier circuitry.<br>
<br>
Unfortunately, the amount of current that flows from small amounts of<br>
radiation is measured in units like femtoamps-nanoamps, i.e. not very<br>
much.<br>
<br>
Another detector that can be made at home is the electroscope that was<br>
also mentioned above. This is the old high-school physics experiment<br>
with the two gold leaves. You charge them up, and the rate at which<br>
the charge leaks off (and they come back together) is proportional to<br>
the amount of radiation present.<br>
<br>
<br>
Here are some links that may help:<br>
<br>
Ludlum Measurements - They sell 100% excellent, new detectors. I'd<br>
recommend a pocket-sized detector with a panckae or end-window tube:<br>
<br>
<a href=3D"http://www.ludlums.com/" target=3D"_blank">http://www.ludlums.co=
m/</a><br>
<br>
Homemade Ion chamber:<br>
<a href=3D"http://www.edcheung.com/automa/radon.htm" target=3D"_blank">http=
://www.edcheung.com/automa/radon.htm</a><br>
<br>
Homemade dosimeter:<br>
<a href=3D"http://en.wikipedia.org/wiki/Kearny_Fallout_Meter" target=3D"_bl=
ank">http://en.wikipedia.org/wiki/Kearny_Fallout_Meter</a><br>
<br>
The best place to find discussions on radiation instruments - homemade<br>
and otherwise:<br>
<a href=3D"http://tech.groups.yahoo.com/group/CDV700CLUB/" target=3D"_blank=
">http://tech.groups.yahoo.com/group/CDV700CLUB/</a><br>
<br>
FEMA course on how to monitor radiation (free self-study online)<br>
<a href=3D"http://training.fema.gov/EMIWeb/IS/is3.asp" target=3D"_blank">ht=
tp://training.fema.gov/EMIWeb/IS/is3.asp</a><br>
<font color=3D"#888888"><br>
<br>
Arclight<br>
</font><div class=3D"im"><br>
<br>
On Tue, Mar 15, 2011 at 9:09 PM, Sean Bonner <<a href=3D"mailto:sean at sea=
nbonner.com">sean at seanbonner.com</a>> wrote:<br>
</div><div><div></div><div class=3D"h5">> Anyone know anything abut geig=
er counters? Specifically building them?<br>
> Have some folks in Japan who are trying to get their hands on them but=
<br>
> failing and considering DIY options...<br>
><br>
> --<br>
> Sean Bonner<br>
> <a href=3D"http://www.seanbonner.com" target=3D"_blank">http://www.sea=
nbonner.com</a> - homebase<br>
> <a href=3D"http://www.metblogs.com" target=3D"_blank">http://www.metbl=
ogs.com</a> - get local<br>
><br>
> *** Please check your address books, the best e-mail for me is<br>
> <a href=3D"mailto:sean at seanbonner.com">sean at seanbonner.com</a><br>
> _______________________________________________<br>
> Discuss mailing list<br>
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