So You Wanna See Atomic Particles With Your Own Eyes Part 4: Inferrence via Ion Induced Voltage Fluctuations (Welcome to the Ion Chamber)
There is more to seeing than what meets the eyeball.
-N.R. Hanson, Patterns of Discovery
We've explored actually seeing the paths of particles in a nuclear cloud chamber; watched corruscating alpha particles slam against a phosphor screen in spinthariscope; watched them explode when crossing the high voltage spark detector; found fields of activity with the radio telescope; and just horsed around with regular old Geiger Counters for fun.
It's time to mix low voltage (8.5v) with soldering, multimeters and aluminum foil to make an Ion Chamber.
Simply put: we charge a cookie tin and have a wire inside that acts as a cathode. As ionized particles enter the chamber they create a current flow that is displayed on a multimeter. The higher the volts, the more ions which means greater radiation.
Cookie tin.
Screws that join the circuit board physically and electricity to the tin.
The cover of the tin becomes a circuit board cover.
I soldered a wire to the middle post of a Darlington transistor. This is the cathode that passes through the bottom of the circuit board and into the tin. The Darlington transistor is actually two transistors in one package. The first part amplifies the incoming current, the second amplifies it even more!
A guy named Sid Darlington actually patented the idea of putting "two or three" components into a single unit back in the early 1950s. Not sure how momentous this was. Um, "let's moosh together two pizzas and make a mediocre double-pizza with a soggy crust center." Yeah, no! I think he actually figured out how to do it though, so it wasn't just the dopey idea of smashing them together that was his claim to fame.
Anyway, it acts
like a single transistor but it amps up (high gain) the input. However the
first of the Darlington ‘pair’ sucks up the voltage and responds in the
circuit, leaving the second built in transistor a little ‘hungry’ for more.
Think
of it like two cats in a single cage: first one gets enough food, the second
doesn’t so it makes for a really jittery pair of cats. That’s generally bad,
but how can we use this to our
advantage?
Darlington Pairs are very jittery = very sensitive! They make create
components in touch sensors. What are we
doing? Well, we’re building a sensor that detects when it is touched by tiny
little ions right? Great! How can we increase the jittery sensitivity of this?
By adding that long wire to the middle leg of the Darlington transistor and
extending it into your ion chamber. Neato!
Here's a photo of the wire coming off the Darlington straight at the camera.
By the way, I ordered the circuit board and transistor from Madscientisthut.com. They're neat people, ship fast and have cool stuff. You can order an ion chamber kit from them in various ways. In one of the kits they'll even through in a multimeter!! Or you can buy the board and source the parts separately from Radio Shack or wherever. I've found that usually on Amazon you have to buy 100 of the same components-it's cheap, but do I need 100 Darlington Transistors for $5 and free shipping? No, that's where kit designers like Madscientisthut.com come in and make everything easier.
I do order capacitors in bulk, because I get weird and blow lots of capacitors. A just received a bag of 100 capacitors from Amazon, which was a good deal and convenient...as you'll see in my next post about linear laboratory bench power supply making (there will be a loud bang and a little smoke!).
Ok, here is the circuit board mounted on the cookie tin.
The inside of the cookie tin with the cathode wire in place.
The open end of the tin is covered with aluminum foil. I roughly zeroed out the meter.
Here is that meter during testing with a uranium test source (upper left above the foil).
Back view of the unit with the circuit board guard off and meter reading 15.1 mV. Notice the vial with uranium placed behind the ion chamber.
I moved the uranium to the front (sensing) side of the chamber. Notice the meter has started climbing.
Here's a nifty video I made of it in action. All of this was done before I properly mounted the circuit board deflector guard.
With the circuit board guard professionally mounted (with two different kinds of tape) I can now turn the unit on and use a plastic screw driver to zero in the unit by adjusting a 10k and a 100k potentiometer through the holes.
Not something I'd have in my carry on luggage, but it works and only took me two nights to build.
The first night I was soldering and half my house went dark. Apparently the 240v electricity from the pole gets split into 120v when it gets to the fuse box. Sometimes with a blown utility pole transformer half the box can go out: either the left side (odd numbered fuses) or right (even numberr fuses) loses power. My basement, garage and half my kitchen worked fine. All the other rooms had dim lightbulbs that slowly went dark.
"How can a soldering iron cause this?!?"
I finally looked outside and saw the street lamps going dark and realized it was a power line/pole problem. For a few minutes as I sat in complete darkness holding a blazingly hot soldering iron I thought I fried my house wiring.
I got to bed at 3am with a power company using a gas-powered generator backfeeding the pole by my bedroom window. Backfed with a regular old orange extension cord up the pole. It's very important to wire in emergency generators for your home properly: if you backfeed your house with a male plug to your wall you can kill a utility worker.
