No subject

Sun Mar 6 13:40:07 CET 2011

It seems as if... if you register anything with that... you have already
taken a lethal dose of radiation.

On Tue, Mar 15, 2011 at 11:31 PM, john arclight <arclight at> wrote:

> I have actually had some training on  this topic, and have a pretty
> good knowledge of radiation instruments.
> What your friend needs is a low-range instrument, i.e. something
> capable of detecting at least beta/gamma radiation from background up
> to 100mRem/hr or so. The big, yellow civil defense units like the
> CDV-715 are high-range detectors that will only register on very high
> levels of radiation, such as the fallout from an actual nuclear
> detonation.
> Unless they are working around that nuclear plant, the worry is not
> direct exposure to radiation, but contamination from particles of
> radioactive material.  Short-term exposure to high levels of radiation
> can cause burns and sickness, and long-term exposure (such as from
> eating contaminated food or breathing in radioactive vapors from a
> steam explosion) can increase cancer risks or damage certain organs,
> such as the thyroid.
> Ionizing radiation comes in three major forms: gamma rays (high-energy
> photons), beta (high energy electrons), and alpha (heavy particles
> with two protons and two neutrons).   Microwaves, radio-frequency
> energy and EMI from power lines are not considered ionizing radiation
> and not hazardous in the same way.
> Radiation exposure can be limited in 3 ways: time (minimize the time
> you are outside, for instance), distance (evacuate the immediate area)
> and shielding (stay inside, put stuff between you and the source of
> radiation).  Gamma rays require mass to stop. Beta rays can be stopped
> by thin metal, and alpha particles are actually stopped by the first
> few layers of your skin. None of these types of radiation will make
> you or anything else radioactive, but you can be harmed if you absorb
> them into your body and they continue to decay and release radiation
> at zero distance and with nothing shielding you from them,
> The type of radiation that turns normal matter into radioactive
> isotopes is only found inside the reactor while it's running (neutron
> radiation) or in a particle accelerator.
> There are several ways to detect low levels of radiation as you might
> find in downwind contamination from the plant. One would be the
> already-mentioned Geiger-Mueller  counter.  It needs a factory-made
> tube with an electrode and a special quench gas sealed inside,  along
> with a 500-750VDC power supply. When a ray or particle of ionizing
> radiation passes through the tube and intercepts a molecule of the
> gas, it will ionize it and cause a spark to jump from the electrode
> inside to the grounded outside, registering a "click" or count.
> All of these tubes will detect Beta and Gamma rays, and some with a
> thin mica window (called a "pancake" or "end window" tube) will also
> detect alpha particles . A pancake G-M counter would be the gold
> standard to acquire.
> A serviceable alternative to the G-M tube is the ion chamber. This
> uses a sealed container full of gas, but it operates at a much lower
> voltage and the gas can be air. It operates on the principle that the
> air inside will become more conductive and pass more current if there
> is ionizing radiation passing through it.  You can in fact make one
> out of a soda can and some amplifier circuitry.
> Unfortunately, the amount of current that flows from small amounts of
> radiation is measured in units like femtoamps-nanoamps, i.e. not very
> much.
> Another detector that can be made at home is the electroscope that was
> also mentioned above. This is the old high-school physics experiment
> with the two gold leaves. You charge them up, and the rate at which
> the charge leaks off (and they come back together) is proportional to
> the amount of radiation present.
> Here are some links that may help:
> Ludlum Measurements - They sell 100% excellent, new detectors. I'd
> recommend a pocket-sized detector with a panckae or end-window tube:
> Homemade Ion chamber:
> Homemade dosimeter:
> The best place to find discussions on radiation instruments - homemade
> and otherwise:
> FEMA course on how to monitor radiation (free self-study online)
> Arclight
> On Tue, Mar 15, 2011 at 9:09 PM, Sean Bonner <sean at> wrote:
> > Anyone know anything abut geiger counters? Specifically building them?
> > Have some folks in Japan who are trying to get their hands on them but
> > failing and considering DIY options...
> >
> > --
> > Sean Bonner
> > - homebase
> > - get local
> >
> > *** Please check your address books, the best e-mail for me is
> > sean at
> > _______________________________________________
> > Discuss mailing list
> > Discuss at
> >
> >
> _______________________________________________
> Discuss mailing list
> Discuss at

Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

More information about the Discuss mailing list