Carl... Duct Tape and Plastic. Sheesh.
"Having a radiation detector like having a smoke detector? If there's smoke you grab the extinguisher or call the fire department. If there's radiation what do you do, by a tent?"
With a smoke detector, its telling you something.
With a radiation detector, it will tell you something that someone else wont.
Both come in handy I think!
RFB
Carl asked about me publishing details of this Geiger Counter. It is not necessary since there are many articles already available from a search of "Geiger Tubes", "Geiger Kits", etc. The HV circuit I used is from this link:
https://sites.google.com/site/diygeigercounter/circuit-description
If you snoop around this site you will find details of the kit they offer for sale. With any kit it is important to understand that the performance will vary according to the tube used. Many kits use surplus Russian tubes which are OK but are not as sensitive as some others which are available.
Here's another site which compares some of the tubes available:
https://sites.google.com/site/diygeigercounter/gm-tubes-supported
The only thing I did in my design which is unique and I have not seen others do is to use a LM339 comparator IC to "slice" the GM tube signal. This allows discriminating between HV supply hash and real discharges.
There are many of the surplus CDV series Civil Defense survey units available for those who want a ready to use instrument at a reasonable cost. With these and any detector do your homework before you buy. Many of these are ionization chamber types which are not suitable for general hobby use since they will not detect low levels of radiation. One hobbyist is quoted "if the ionization chamber meter indicates any counts then it is time to leave the area." Make sure you get one with a GM tube probe for general use. Carefully read all you can about this before you buy.
I don't know a lot about ionizing radiation so I hesitate to give any specific advice other than what I have done. I can advise on the circuitry and tubes but not beyond this.
Neil
Is your prototype detector detecting anything?
Not sure what you mean by this but I did do an experiment this morning with the scintillation detector. I have made a box filled with 20 pounds of lead birdshot and some sheet lead which surrounds the detector to reduce the background counts. It has dropped the counts from about six to eight hundred per minute to 12 per minute. This is similar to the signal to noise problem in radio. In order to hear the desired signal the noise has to be reduced.
My experiment was to use a special fan powered dust collector to gather a sample of household dust. This collector is also known as a clothes dryer and the sample as dryer screen lint. The count, accounting for the background, from this lint sample is 24 CPM which is very low compared to the background. House dust is known to contain radioactive matter and I suppose ours does.
I have kept an informal and unscientific log of the background radiation here, both indoors and out, for a few years and have found no difference between indoor and outdoor and no time related trends. Based on this, there is little impetus for me to formalize this unless something happens which could affect the counts.
The other problem with this activity is calibration. Right now the best I can do is measure the counts per minute but it is not possible for me to convert this to biologically meaningful information such as rads or Sieverts. Calibration sources are available but I prefer to avoid the expense and storage problems associated with these. Reminiscent of the field strength calibration problem isn't it?
Neil
This thread opened with a display of a prototype circuit followed by more examples of prototype types, then the mystery prototype was revealed to be a detector for low level radiation, so I called it a "prototype detector." Of course I did not think it could detect prototypes.
But all that language aside, it is very interesting, and it now appears, from readings you have been able to achieve with the device, that Fukashima and other sources are not necessarily raising the ambient radiation level around the globe as I, for one, have feared.
Here's a science question that ties into the subject of radiation.... How does a Radon detector differ from what you have built?
Carl, the only radon detector for home use I know of is an activated charcoal canister which is placed in a specified area for a specified time and then sent to a lab for analysis. The key to getting a meaningful radon reading is to separate the radon effects in the canister from other effects. This is done with a radiation mass spectrometer which detects and identifies the decay products from the radon. This is way beyond what I can do here.
I do plan to try to design and construct a multichannel analyzer which generates a histogram of the number of counts vs the energy. The voltage output from the photomultiplier tube in the scintillation counter is related to the energy of the radiation particle which causes the scintillation in the NaI:Tl crystal in the probe. I have the hardware and software to measure the voltage but the problem is that the pulses are 200 nanoseconds wide with amplitudes from tens of millivolts to 6 volts. The hardware and software is just not fast enough to capture these accurately. Very high speed analog circuitry is needed to pre-process the signal for computer sampling. The most easily workable scheme I have come up with is to construct a discriminator using a dual comparator with a discrimination window set and varied by the computer and the event stored in a flip-flop. This removes the real time constraint of the software. Even with missed events due to refractory time of the device, over time those captured will average out to give a good histogram showing the relative energies present. The actual counts will not be accurate but the relative counts in each energy slot should be. A flash A/D converter could work better but it is more complex
A geiger counter operating in the tube "geiger' region as is customary cannot discriminate the energy since the amplitudes are all the same.
Yep, there has been severe thread drift from the topic of prototyping but I don't mind sharing the technology beyond building. I see this type of activity as exercise for my brain.
Neil
Neil, I'm absolutely fascinated by the way you are trying to "see" (measure) such a hidden set of events intertwined with what we call "nature."
The time factor alone is such a moving target (fact not pun) and the tiny increments you talk about are way deeper than the frequency drift we experience with RF.
Speaking of energy, my thoughts always latch onto another puzzle that torments mankind.... we are surrounded by infinite energy, but converting it to the right form is the trick.... how to make heat in cold weather, for a very prominent example. And going way the heck off thread, I wonder if cold is a form of energy? Heat is, so why not? What if cold could be flip-flopped and become heat?
Now I'm starting to dream.
The point now is, your explorations are inspiring!
I have designed a digital circuit to process the signal from the scintillation counter. The circuit accepts two analog voltages from the PC to establish an amplitude window for the PMT pulse and strobes a counter line to the PC when the pulse amplitude is within the amplitude window. This pulse duration is 200 nanoseconds so the circuit has to respond quickly.
But the purpose of posting is to show another prototyping/final build method with a picture linked here: http://postimage.org/image/3o476d1zx/
This is another "dead bug" build but since these are digital chips there is a different approach to interconnecting than with an analog circuit where interconnecting wires are used much less typically. For digital most of the connections are interconnect wires. Borrowing some things from wire wrap construction this board was made with wire wrap wire which was wrapped around the IC pins using a wire wrapping tool. The connections were then soldered. There are several connections to the outside world so small squares cut from priinted circuit board are glued to the board and provide isolated pads for connections.
The "plate of spaghetti" or perhaps scrambled eggs appearance of the wiring is actually an advantage for high speed digital circuits. Wires which run parallel can inductively couple signals from one node to another but running them scrambled minimizes the cross coupling. The PC board also provides a ground plane which is advantageous for high speed digital signals. This also saves the cost of conventional wire wrap sockets which usually cost more than the chips they hold.
The small green objects are .01 uF bypass caps which connect from VCC to GND at each IC to suppress power line transients when the ICs switch state. Good documentation is needed for this type of build since the wiring is very difficult to trace if the schematic becomes lost.
This circuit uses 74LSxx ICs which are very high speed and switch in tens of nanoseconds. This is why layout is important to minimize errant operation caused by power buss noise and cross coupling and ringing.
I hope this gives you some ideas for another prototyping method. Now I am off to program the computer to work with this board. For me, this is not a much fun as messing with the hardware but it is a necessary means to an end.
Neil
Impressive work.
Really interesting!
Bruce,
DOGRADIO STUDIO 2
The latest prototype and it's function is so interesting.
It would be very easy to make a circuit that looked more or less the same, but if I made it it wouldn't actually do anything, unless by accident I invented a time-machine or something.
Knowledge..... that's what does it.
Despite a few glitches and the need for tweaks the device works as planned. Here's a screen shot of the software generated data display based on the counts received from the discriminator circuit.
http://postimage.org/image/5jvkv9g7x/
The scintillation detector is really singing with over 1000 clicks per second being detected from a test source. The red on the scale of the meter means nothing...it is just one of the meters built into the software and I have yet to change the colors.
Now I need to find a box to house the circuit and this project will be a wrap.
Neil
It is fantastic, Neil! It is goose bump city. A beautiful piece of work.
In past years I worked for a music station whose slogan was "The Scintillating Sound of 77-WEW......" At the time I never quite knew what that actually meant in terms of listener experience. What we needed was your "Scintillation Meter" to see how it was going.
This is the frequency range of gamma radiation which is on my mind as residue from my scintillation detector project. As I ponder this it is remarkable how similar this is to radio measurements, especially the spectrum analyzer.
The detector with a window discriminator does the same thing as a spectrum analyzer except for the frequency range covered.
It works by measuring the peak voltage for each pulse from the detector. This voltage is approximately proportional to the energy of the radiation and the energy of radioactive particles and waves is related to frequency by the DeBroglie wavelength. Essentially, the higher the energy the higher the frequency. So, sorting the pulses according to voltage is the same as sorting them by frequency such as a radio frequency spectrum analyzer does. Also as does the spectrum analyzer the information can be plotted as a histogram (spectrum display) of counts vs energy yielding the energy distribution.
Here's a link to the displays created by the software I just completed for this project:
http://postimage.org/image/6hfs9cvvh/
Each display pictured is from a different radioactive source. What is very useful about this is it shows a different "fingerprint" for each source. Working backwards, it is possible to identify the source from the display pattern.
The peaks represent the energy peaks which are characteristic of radioactive elements. This goes beyond the similarity to radio work since it is also the same principle used in many scientific analyses such as spectrophotometry in chemistry and astronomy.
Back to radio it is also similar to a graphic equalizer in reverse. Instead of setting the spectral plot this device measures it.
Well, if you have stuck with me so far then I hope the reads were worthwhile. As with many things I found that the deeper I dig into a project such as this the more I realize I don't know but it is fun to pursue nonetheless.
Neil