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Radio-active indicator ?

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I would like to make some sort of
ionising radiation detector.
Anyone have any suggestions?

Some sort of geiger counter,
but it doesnt have to count.

Just some sort of indication.

Hey John - I can't believe you are looking for this. I ran across this schematic the other day

**broken link removed**

there is no text or information but maybe it will help.
Thanks Gene,

The detector in that circuit is a GM tube.

I would like to make some sort of detector.

I thought maybe ethanol vapour under suction,
with a voltage on two electrodes might do,
but i dont know enough about it.

It doesnt have to be like that,
i also wondered if phosphorescent powder
might do, if the emission could be amplified
from a photo-transistor.

I would consider any form of indicator
that i could make.

Perhaps the physics department at your local university can help you with the detector - if you tell them what type of radiation you are trying to detect (alpha, beta, or gamma), and the energy level / frequency you are looking for.
Nuts and Volts magazine had a schematic for a little geiger counter that used a neon bulb. The circuit used 10 9V batteries in series, a 91V zener across the batteries, a 100K pot in parallel with the zener, then a 200K Resistor from the wiper to an NE2 and a speaker to ground. You would adjust the pot so the neon would just turn off.

Looks neat, I haven't tried it though.

Jan 2003 issue, page 25
This is a wild shot. Some home smoke detectors detect the flow of radioactive particles (the interruption of the flow by smoke is the trigger). Is it possible to use the detector circuit/device from one of these to detect the presence of radioactivity?
Hi Gene, Sounds interesting, but the smoke alarm circuitry
would have to be altered if the unit could be triggered by
any radiation or particle,
because the smoke alarms ive seen have to be manually reset
to stop the alarm,
However maybe the sensor could be used in that way.

Ive just re-read your post, that sounds complicated ...
they expect so see background radiation to remain quiet ?
I don't know how i would alter that, maybe if i studied the
schematic of one, it might be possible to take the sensor
reading to a moving coil meter instead of to the trigger
mechanism part of the circuit.

Its quite likely that the whole shooting match has been
compressed into a dedicated chip, so some knowledge about
the sensor would be needed, i guess a DC signal amp would
be a first step. Actually no, finding out which alarms use
a system like that would be first, that might be hard to
find out.


Hi lavenatti, i am glad you posted that because i was
thinking of trying a neon bulb, but i was put off because
i read that the 'window' has to be very thin to admit any
ionising particles or radiation.
It sounds exactly the circuit that i would have made.

I would have the neon bulb biased to turn on, but not lit
i guess that the nearer to striking you adjust, the more
sensitive it would be.

Once lit, i would suppose the series resistance would be
such that it could not maintain itself, and would go out.

I suppose a small cap could be put across it to ensure an
audible click.

I think i will start doing some experiments along these
lines. I dunno what i'll use for a source though, maybe
the front of my telly. I think the electrons fly past the
screen for an inch or so, till they're lost in the air.
Whether or not they will do what radiation does i don't
know. I am thinking of low-level radioactivity, such as
power generators or from submarines.

Many thanks to you all for your interest and input.
This is the sort of thing i had in mind ...


  • Geiger.jpg
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Interesting that I see this kind of request, because I was actually discussing the building of an radiation detection circuit with my physics professor. He has a design that involves an aluminum can, argon gas, and the scrapings off the mesh that burns in a gas lantern. I have no idea how it works, but he said he has a working design, and that all I had to do was to come up with the logic to detect the interation of the radiation particles with the biased wire that runs through the can. I'll talk to him and get this design as soon as I can get ahold of him then let you know what the whole design is.
Ionising Radiation ?

Hi John1
You mention using a CRT as a source of radiation ... Nope, won't work.

Alpha/beta/gamma radiation will attempt to disloge electrons in a detector's chamber (inside the neon's envelope?), the bias field hopes to encourage these odd electrons to migrate and result in a current flow.
I don't see how stray electrons entering the chamber can cause the same effect.

Use a cheap 'ionising smoke detector', they contain a #very weak# radioactive source to ionise smoke particles in free air, a small current is thus generated but the process is the reverse of a Gieger tube ... ?
Also granite rock is radioactive, so are old (1940s?) watches with phosphor dots (glow in the dark).
The glass on the neon bulb probably would stop a lot of the radiation. Alpha particles are stopped by a sheet of paper.

A small flourescent tube may work better, thinner glass, much larger area.
A small florrie is an excellent suggestion.
I will be making one like that soon.
Dunno what i will use as a source,
i will let you know how i get on.

Cheers, John :)
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