A call to arms

Seeed Studio is asking for help creating an open source radiation sensor, to help in the wake of the Japanese Tsunami earthquake.

Can open hardware community do something to help in this? Seeed Studio is now sourcing sensors, then assemble quick measurement tools,  ship as many/fast as possible to Japan.

Since we have no previous experience with such device,  your help is needed!

If you have experience in making such device, some quick questions:

1. What would be the right sensor for such detection? Will the education purpose GM tube work?

2. Any recommended peripheral circuits?

3. Does such Geiger counter needs special calibration? Or can we calibrate it with commercial device?

All creations will be open source and donated, thank you for helping out!

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  1. There’s a Yahoo group that has some relevant info:

    This page describes how to build an ionization chamber, intended for detecting Radon gas, but I believe it would be sensitive to radioactive fallout also. It is really quite simple and does not require any exotic components. Of course, you need something radioactive to test it with, and even if you do calibrate it, the calibration probably drifts with time.

    The only manufacturer of geiger tubes I know about is LND in New York. In normal times, this is a pretty specialized component. http://www.lndinc.com/

  2. Here is a DIY radiation detector I made. Out of a smoke detector and an arduino.
    I made this in about 20 minutes for a physics class. If you spent more time i’m sure you could make something more accurate and cheaper. The smoke detector only cost 8$ dollars to begin with. A few corrections to the video. Its pins 1 & 3 on the smoke detector chip which i believe is a mosfet, and Americium-241 is a radioactive alpha source which i don’t think i mention in the video.

  3. Hi there,
    To begin with, there are two ways of measuring the radiation electronically (not physically):

    1. by using of GM (Geiger-Muller) counter. GM counter utilizes special GM tube, that is filled with inert gas, and is capable of detecting single ion. As tube is driven by high voltage DC, single ion will cause the discharge. Tube is driven through series resistor for current limiting – counter uses it as a shunt to measure voltage drop on it. When discharge occurs, there will be some drop on it, and counter increments the count.

    + There are no calibration needed for this method.
    + It’s more efficient for Gamma rays.
    + Exact measurement of radioactive flux is calculable from amount open surface of tube.
    + You just need to add timer to the counter, and after certain time (depending of openings size of tube) the count will represent actual value in micro-Roentgens .
    + works with very small amount of radiation
    + No isotope needed for testing. Natural radioactivity on the surface of the planet is about 10 to 14 uRoentgens, and you can measure this with GM tube with some 200ppm precision, if using 100ppm oscillator timebase.
    + with small size GM tube, you still have very nice response
    – no response to alpha particles
    – bad response to beta particles
    – Expensive
    – slow measurement for exact value.
    +/- complex DSP algorithms can estimate exact value of flux in short time and gain accuracy over the time of continuos measurement. (Ask me on the email, if you’d like assistance with those).

    2. ICh (Ion-Chamber) sensing element. That’s the one [punkysfan] is using from the smoke detector. This is very simple sensor – it’s stated to be gas-filled, though in this case gas is oxygen mixture (air). Here, in Europe, we do not use this type of gas sensor (because of radioactive bias current source inside), so I cannot evaluate exact precision or stability of this circuit, though it will work for sure, as the ICh is nothing more than 2 electrodes with gas in between them. Then again – you should always remember, that ICh based radiation measurement is _NOT_ a counter. As ICh does not detect a single discharge, you’ll have to measure the electricity, generated by the continuos ionization of ‘air’ by radioactive flux.

    To do this, you need one of three: galvanometer, Coulomb counter or trans-impedance amplifier + ADC.

    + Cheap, simple, can be made of 2 metal plates or pipes surrounded with air.
    + Responsive to alpha and beta particles
    + Larger dynamic range in the higher radiation, than GM tube
    + Faster response (due continuos flux measurement)
    – Not so sensitive, as GM tube (measures flux, not single particle)
    – analog measurement: must be calibrated
    – Need of isotope for test / calibration (potential exposures of personnel)
    – Precision affected by all types of RF interference
    – to get good response & accuracy, you’ll need considerable size of ICh

    Well, this is a short form of the comparison, just ask me on the email, if you need more in-depth help with choosing of sensor type. My personal preferences are GM for measurement devices and ICh for detectors / indicators (if we’re talking about civil / consumer apps).

    When you have chosen the sensor, you are free to ask me help with measurement algorithms and HW implementations for specific type of sensor. In case of GM counter, I do insist of PLD implementation. Compared to any MCU implementation, there _is_ a way to make precise counter w/o lost samples or timer lags.

    Hope the info will be useful to you and together the community will be able to help Japanese people.

  4. By the way, this gives me an idea – if there would be reasonably priced radiation measurement sensor (GM tubes preferred) available, it could be possible to make and deploy small sensors around the world and sync the data in real time on a web page.

    If someone is up to hosting / arbitrating such project, I am willing to participate with R&D, ASM, Verilog, PCB design an Testing. And I’m willing to host few of such stations at Latvia, of course. Also, we can add temperature, rainfall, humidity, wind direction and speed, etc sensors..

    As renewable energy harvesting becomes popular, we can measure also the solar intensity for photovoltaic harvesting and later there can be all kinds of statistics and real time data at the website..

    If someone’s willing to donate a cray computer, we can make forecasts too :-)

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