DIY Thorium detector (ion chamber)

[zoomkat]

My transistors came today so I put together a simple ion chamber to see if it worked. It works pretty well considering it is mostly a coffee can, Darlington transistor, HF multimeter, 9v battery, and some wires. In the pix below you can see gold top mantles (and butterfly mantles) stayed at the background value of 20-25mv. The Aladdin #200 mantles had a reading of ~470mv, so I suspect they contain Thorium. Pretty simple setup if you can solder electrical components.

[CraterEddie]

That's a neat project, thanks for posting.
I had wondered about the Chinese Butterfly mantles since they are so bright, although the listings do say "non radiative".

[Gunhippie]

Schematic? I can't quite make out the tangle of wires.

Looks like a cool project for an afternoon.

Do you put the mantles inside the can? Thorium is mainly an alpha emitter, so I'd think the can and lid would block almost all of them.

[DougA]

Yes, a schematic would be great. I also love to see that someone else builds electronic projects with scraps of old telephone wire, too! ?

[CraterEddie]

This looks like a good resource:

http://www.techlib.com/science/ion.html

[zoomkat]

Below is the schematic and there is some youtube stuff (and google) on making these. I just put the mantles inside the can and put the lid on to keep the air in so it will reach an equilibrium ionization state for a better reading. I'm going to make a more compact version with a thin membrane (saran wrap) over the face to see how well it works for putting it over things. I used an inexpensive MPSA13 Darlington transistor from ebay. I've got some MPSA14 transistors on the way that might have twice the gain, but the MPSA13 seems to work just fine for this. Per writeups of others, the 4.7k resistor is just for short protection if you touch the wrong things together, so it may not actually be needed if you are careful. A simple project to answer some of the "Thorium" questions about various mantles.

[Gunhippie]

Cool! Thanks!

[outlawmws]

Darlingtons will triple in cost in the next week! ?

Cool project!

[Bob1774]

Cool!
Got to trust anyone who keeps a Schrader Valve tool on their bench.

[Gunhippie]

[QUOTE username=outlawmws userid=4669281 postid=1309477763]Darlingtons will triple in cost in the next week!

Cool project!
So, up to about $0.45 each?

[Gasman64]

Very interesting project, ZK, thanks for the pictures.

[zoomkat]

Might be an opportunity for OCP to develop a basic DIY science education kit consisting of a transistor, a resistor, and a "radioactive" lantern mantle. The mantles are the hardest part to come by. Or maybe include a bonus transistor and resistor with orders over a certain amount for the "enthusiast". ?

[outlawmws]

I was looking at the schematic, and since the tin can is "hot", I can see where the resistor makes sense.

Since this is radiation we are talking about I assume you could test mantles still in the package?

I need to find my transistor and IC collection, I bet I have a Darlington or three somewhere... (Usually all I need are resistors, caps and LEDs - those I keep handy...)

[zoomkat]

"Since this is radiation we are talking about I assume you could test mantles still in the package?"

You can, but the reading will be significantly lower. Two Aladdin mantles in the package will only raise the reading from something like 10 to 40 (but you should be able to detect a noticeable change in the reading). two Aladdin mantles out of the package can read 400+. I imagine the plastic package blocks most of the alpha particles, with maybe only beta particles from the alpha decay daughter products getting thru. With Radio Shack gone, getting electronic parts in timely manor without a lot of shipping cost can be a challenge. If you just have the transistor, you can assemble the detector without the resistor, and then check for a short using the multimeter in the resistance/continuity mode on the leads that connect to the battery.

[zoomkat]

I checked a Golden Anchor mantle and an Egret 300/400CP mantle. The Golden Anchor was only about 12mv (background), but the Egret produced around 200mv of activity. I just looked on ebay and somebody has been selling them BIN for 60 for $39.99. The person has a picture of a radiological readout from a measuring device. Might be good for the larger single mantle lanterns, but I don't know their overall quality and have not tried them.

[philbotha]

A Darlington Pair is just two ordinary transistors wired together that way. It multiplies the current gain of the two transistors, meaning it is a very sensitive current amplifier. The tiny current through the ionised air (caused by the radiation of the mantles) to the base of the darlington is multiplied and measured at the collector by the meter set to the milliamps (microamps?) range. Et voila, a radiation detector.

Good for a relative or go-no-go test. It will be very susceptible to moisture in the air and to any sources of electrical interference.