Geiger Counter Build

publius · October 31, 2014, 6:20pm

If you mean to sign up for the Geiger counter build project on the 15th, here is the link :

I ordered 15 tubes, so assuming one for the 'Space, one for me, one for a second instructor, that makes 12 for everyone else. Since the class was set up with 10 tickets on Eventbrite, that means I can accommodate two people who would prefer to pay the materials fee to me directly.

publius · October 31, 2014, 6:33pm

User Interface question :
Is an audible indication important? If so, should it be a click or chirp, or possibly a buzz or tone which changes in pitch with the counting rate? I am thinking a log-scale change in frequency might work.

Opcode · October 31, 2014, 8:01pm

I would like to have an audible click to measure the detection rate. It’s handy having the extra sensory input, especially if I would want to use my eyes for something else. It would also be nice to have a switch to turn it off, if necessary.

publius · October 31, 2014, 8:06pm

An audio-off switch is necessary for battery conservation. A display-off switch might also be a good choice. The two could be combined, I think (center position both on, one outward position display-only, the other audio-only).

william_petefish · October 31, 2014, 8:14pm

On a related note,

Do you think that a scintillation counter build would be possible in the future?

publius · October 31, 2014, 8:35pm

From my point of view, it depends on the level of interest.

I’ve bought enough tubes to make fifteen G-M counters, & am getting ready to buy the rest of the components, but so far only three people have paid the Eventbrite materials fee (even though a number of others have said they were going to sign up). Hence I’m seriously concerned about taking a bath on this project, which is going to deter me from similar proposals in the future.

So far as a scintillator instrument is concerned, the main value lies in its gamma-spectrometry function, which allows identifying radioisotopes. That seems a lot more specialized than a simple radiation detector. I agree it would be a useful thing to have, & I’ve thought about it a bit, but I don’t know how much money I want to sink into it.

jesse · November 1, 2014, 2:34am

I’m very interested in this class. I don’t know how to solder, though - I have done it once, but that was years ago. Would that be an issue, or is it something I could pick up fairly easily as we worked on the build?

Thanks!

Jesse

publius · November 1, 2014, 4:28am

I’m working to minimize the amount of soldering required for the design. The high-voltage section is going to have some surface-mount components, & that will have to be taken care of beforehand. Better for safety anyway.

Opcode · November 1, 2014, 4:50am

I learned MILSPEC, Aerospace-grade soldering twenty years ago. I’ve forgotten a bit since then, but I think I could get you through this class.

Opcode · November 1, 2014, 4:55am

I would like to participate, but I’m right on the edge financially. I finally got a job after a year of unemployment. The longer I keep my job, the more likely I am to participate in something that requires payment.

publius · November 1, 2014, 5:06am

Frankly, I’m a lot better with theory than I am with soldering, which is one reason I was looking at recruiting a second instructor to assist with some of the practical parts. The main perq of this would be essentially being comped the materials fee.

rice81 · November 3, 2014, 3:52pm

What are the specs on the counter we would be building? How does it compare with others available?

publius · November 3, 2014, 7:45pm

What exactly do you want to know?

The G-M tube we will be using is the STS-5, a Soviet product which (with the very similar SBM-20) is probably the most common tube used for amateur/hobbyist counters. Length is 110 millimeters, diameter 12 mm, or just about 4 inches by 1/2 inch. This type tube picks up gamma & hard beta radiation, but not alpha (might be made to respond to neutrons by wrapping in cadmium foil). It isn’t the most sensitive tube out there, but its sensitivity is reasonably high, with natural background being typically in the range of 25-35 counts per minute. For gamma radiation emitted by cobalt-60 & caesium-137, the conversion factor for sensitivity is generally quoted at 175 counts per minute per microsievert per hour.

The counts will be registered, user-selectably, by a three-digit LED display in two ranges (x1 and x100 counts per minute) and by an auditory signal (click). The total device will not be much larger than the tube, & will be powered by a standard 9-volt battery.

rice81 · November 3, 2014, 8:39pm

Thanks. I’m interested, just trying to figure out if I have the bandwidth to attend.

Opcode · November 3, 2014, 10:07pm

I’d be happy to help, and it would help me get back into practice. I haven’t done much electronics tinkering in a long time. It’s a shame, because the “E” in my LEOT degree stands for “Electronics,” the main focus being power electronics for laser power supplies.

publius · November 4, 2014, 6:24am

I’ve selected a piezoelectric sounder for the audible element. The spec sheet wants to drive it with a 4 kHz square wave, but in parallel with a nice (say 10 k) resistor hung from an open-collector output of the CPLD, it should make an entirely acceptable click.

publius · November 6, 2014, 1:41pm

Geiger tubes are here!
I expect to spend much of next week at the 'Space, fabricating the circuit boards & enclosures.

Opcode · November 6, 2014, 9:10pm

If I can find time, I’d like to help. Do you plan to spend all day at the Space, or are you planning to spend a few hours at home to sleep?

rice81 · November 6, 2014, 11:26pm

What sort of boards are you fabricating? Laser printer transfer / etchant? Single side? Maybe those in the class should do the work unless you think that there will be a time constraint. There also may be a problem with yield for first time board makers.

Just thinking of a way to limit your work and add some training. If folks have not made a board, then it is a good thing to do at least once. I realize that making one board is a class in itself.

Thanks for your work on this!

publius · November 7, 2014, 5:39pm

I think the most straightforward response is that I expect to spend
extended periods each day, from Tuesday onward, at the 'Space.
Camping out is not something which is exactly supported!

The Stars Are Ours!

 --publius--