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Open Radiation Detector

Quickly identify radioactive materials with a pocket-sized ion chamber. Built from standard parts for easy manufacture and low cost.

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Radioactivity is invisible and can be harmful to life. The goal of this project is to provide a simple device that could prevent cases of radiation poisoning. Professional radiation meters can be very accurate, but are also expensive, complex and fragile (most use vacuum discharge tubes made of glass). However in many occasions we only want to determine whether an object is radioactive or not.

This device uses an open-air ionization chamber with a simple amplifier circuit. It is based on the brilliant work by Charles Wenzel & Alan Yates (http://www.techlib.com/science/ion.html & http://www.vk2zay.net/category/30) among others.

The main innovation when compared to existing meters is the novel ion chamber design, made with PCB technology and standard low-cost components.

Disclaimer

This is an experimental design, at the moment IT MUST NOT BE USED IN CRITICAL APPLICATIONS. The author(s) of this project are not liable for any damage or responsibility derived from the use or misuse of the Open Radiation Detector. 

Challenges addressed

The project started as a personal challenge to build a true low cost radiation detector. For this we needed to tackle the following problems:

  1. Decide the detection method among all the options (see log entry 1).
  2. Design prototypes and test them to assess performance (see log entry 4).
  3. There were problems with electrostatic affecting the measurements. See how we solved it in entry 6.
  4. Thorough the whole project, optimize the design for pick-and-place manufacture with the least components possible.

List of specifications and how they will be met

  1. It must tell if an object is substantially radioactive. There is a lack of low cost options to measure alpha radiation (see log entry 1: introduction to radiation detectors). We decided to go for a ionization chamber design for the following reasons: as opposed to other detectors, ion chambers are simple and don't require high voltages, any vacuum tubes nor delicate mica windows. Still, they are really good at detecting alpha radiation (see log entry 2: DIY ion chambers).
  2. The Open Radiation Detector must be small and low cost. We have already gone through many prototypes and iterations: a spark detector, and many different shapes of ionization chambers (see the log entries).
    1. It must use standard, modern components. Existing DIY designs that can be found online are great, but they rely upon old transistor models that are difficult to find. For this project we have studied more up-to-date options (see log entry 5).
    2. Preference goes to facilitating pick-and-place assembly. Existing DIY projects use recycled tin cans and hand-made parts. We have designed an ion chamber that is built with low cost SMD components and can be assembled with pick-and-place machines. These components originally had completely different purposes, but we arranged them to work as an effective ion chamber (see log entry 4).
  3. It must be open source. We don't believe in patents, specially in the field of safety. The on-line maker community is the best place to share this design and ensure that it reaches the places and applications that may benefit from the Open Radiation Detector.

Will it be world changing?

The goal of this project is to facilitate the identification of radioactive hazards by creating a low cost & mass-producible detector.

Like it or not, the world has become more and more radioactive since the discovery of nuclear energy. Containing radioactive waste is a real problem, and some nuclear disasters have shown us that we live closer to radiation than we think.

The Open Radiation Detector can tell if an object emits dangerous levels of radiation (these are often imperceptible - radiation doesn't glow like in movies!). Our hope is to be sensitive enough to tell if food is contaminated, though we don't know how to test this sensitivity yet. The detector could also be placed in low-cost swarms of disposable robots that roam around a disaster area and mark the hot spots that should be avoided by humans.

We have shared a novel design that uses standard components and can be assembled by pick-and-place machines. There are similar DIY radiation detectors out there, but none of them can be mass-manufactured consistently at such a low cost.

How it works

The detector uses an open-air ion chamber polarized with a transistor amplifier circuit that notifies if high radiation levels are present.

Check out our log entries for more information:

  1. Introduction to radiation detectors
  2. The background: lots of DIY projects
  3. First attempts: an alpha spark detector
  4. Ionization chamber prototypes
  5. Correcting the effect of temperature
  6. Reducing the effect of static electricity
  7. The hand-held detector
  8. Schematic for the amplifier circuit
  9. PCB electrode...
Read more »

BOM_open_rad_detector_0.9.pdf

Bill of materials. Check the GitHub repository for the source file.

Adobe Portable Document Format - 37.96 kB - 10/21/2017 at 14:12

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layout_0.9.pdf

PCB design. Check the GitHub repository for the KiCad sources.

Adobe Portable Document Format - 214.75 kB - 10/17/2017 at 09:54

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schematic_0.9.pdf

Circuit design. Check the GitHub repository for the KiCad sources.

Adobe Portable Document Format - 64.61 kB - 10/17/2017 at 09:54

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  • 14 - HaD prize results + Want to get a detector?

    Carlos Garcia Saura11/13/2017 at 19:21 0 comments

    It was very rewarding to see our project reach the top 10 from the >1000 entries to the Hackaday prize :-)

    Technology needs to be free for all, and this is only possible with a well motivated and supported community of makers. We are very grateful to Hackaday for organizing such a big contest to promote open projects. We are also thankful to the Open Source Hardware and Software Demonstration (OSHWDem) that took place La Coruña (Spain) this weekend, it also contributed to a great diffusion of the Open Radiation Detector and many other projects.

    Some people has contacted us to test the detector with Radon. We will be manufacturing a batch of improved sensors in the near future that shouldn't require calibration and have a digital interface. Get in touch if you are interested!

  • 13 - Working on a new version

    Carlos Garcia Saura10/30/2017 at 23:38 0 comments

    We are working on a new design that improves upon versions 0.9 and 1.0:

    • It will have rear-facing LEDs to allow easy readout from both sides of the detector.
    • Instead of using a Darlington arrangement as the frontend, we are investigating whether it is possible to directly use a really good operational amplifier. This should have better linearity, temperature stability, and maybe allow calibration.
    • Also, it will use an SMD buzzer to further facilitate pick-and-place assembly.

    For the frontend amplifier, we are using the µCurrent by EEVblog as a reference.

    Do you have any ideas on how to improve the design? Please share them in the comments!

  • 12 - Hackaday Prize entry video

    Carlos Garcia Saura10/19/2017 at 11:44 0 comments

    Edited 21/Oct/2017: We are very excited to be on the Hackaday Prize finals! Thank you Hackaday for this great opportunity to share our project with the world :-)


    We have released all the documentation available for versions 0.9 and 1.0. Please let us know if you are planning to build the project and need any more information!

  • 11 - Sources are available! Next steps

    Carlos Garcia Saura10/16/2017 at 15:36 0 comments

    After testing the prototype and making some minor corrections, we have released the KiCad sources and BOM for version 0.9. Bear in mind it is still a very early version of the detector, suitable for tinkerers only! Here is the link to our GitHub repository:

    https://github.com/CarlosGS/open-radiation-detector


    We are already working in the next version of the detector, one that supports the buzzer and a row of LEDs that represent radiation intensity with a scale. (a strip will be much easier to read than a single led's brightness gradient).

    I want to take this opportunity to thank Hackaday for promoting the creation of open source projects. The Hackaday Prize has been the biggest motivation for me to advance this project, document it and finally release it. I really hope this project can help to lower the cost and facilitate the detection of radiation sources worldwide.

    I also want to thank the Grupo de Neurocomputación Biológica at Universidad Autónoma de Madrid for providing the material resources to create the prototypes, which have accelerated the project a lot.

    Finally, the project has reached a point where the power of the community will help take this project to the next level. Did you find the project interesting? Do you have any suggestions to improve detection effectiveness? Please share your thoughts in the comments!

  • 10 - It works!

    Carlos Garcia Saura10/15/2017 at 01:37 0 comments

    The prototype has been successful! Our latest prototype can measure radiation from the source in a smoke detector.


    At first the signal was too dim and we needed to adjust the circuit's gain, after that the sensor could work by itself and notify with the on-board LED (link to video).

    We were most excited to see that electrostatic fields now do NOT affect the measurement! So all the modifications since last version have been for the good :-)

  • 9 - PCB electrode design

    Carlos Garcia Saura10/14/2017 at 10:01 0 comments

    Here are some detailed pictures on the construction of the most important part of the detector: the inner amplifying electrode.

    The central electrode is a surface-mount stud that captures the tiny ionization currents within the chamber. It is tightly coupled with the Darlington transistor that amplifies the signal (see the previous log entry for the schematic), this is done in order to reduce electrical noise.


    Here is how the electrode assembly looks with the shielding can removed:
    On the bottom can be seen the instrumentation amplifier that conditions and further amplifies the signal while compensating for the temperature effects (see entries 5 and 8).


  • 8 - Schematic for the amplifier circuit

    Carlos Garcia Saura10/11/2017 at 22:57 0 comments

    Signal amplification and conditioning has been implemented with the following circuit:

    Amplification is achieved with a pair of Darlington transistors, one to amplify the radiation signal and the other to compensate the effect of temperature over transistor gain (see log entry 5).
    Further amplification and signal conditioning is achieved with an instrumentation amplifier. As opposed to operational amplifiers, instrumentation amplifiers produce an output that is linearly proportional to the difference between the input voltages. This allows to compensate for temperature, amplify and drive the output signal, all in a single step.

    An important detail to note is the need for R5 to tune the output voltages. In theory both signals should be equal when no radiation is present, but we have observed that this is not the case due to transistor manufacture tolerances. If the reference signal is greater than the output signal, it could inhibit radiation detections in some circumstances.
    In our tests we have seen that Vref is usually higher than Vsignal, so it was necessary to place an R5 that drops Vref slightly.

    There is also a potentiometer (RV1) to allow the rescaling/calibration of the output signal, the maximum can be mapped to any value in the 0-5V range. This allows direct interface with Arduino and other platforms.

  • 7 - The hand-held detector

    Carlos Garcia Saura10/11/2017 at 00:15 0 comments

    This project provides two different things: a new design of manufacture-friendly ion chamber, and also a proof-of-concept device that demonstrates its sensitivity to radiation.

    From the start, the idea has been to create a hand-held detector that can be used to check if an object is radioactive or not.

    The sketch on the left was made at the start of the project. Next to it you can see the latest design :-)

    As mentioned in the previous log entry, the ion chamber design has been modified to have a positive electrode that is smaller and placed in central position.
    Next entries will show more details on the schematic.

  • 6 - Reducing the effect of static electricity

    Carlos Garcia Saura10/09/2017 at 22:45 0 comments

    A big problem with our initial ion chamber prototypes was that any nearby electrostatic fields had a large effect over the radiation measurements.

    Even the temperature-corrected version of the radiation detector was unusable: it produced false detections when bringing a charged pen near the detector (a harmless plastic pen that had been electrically charged by rubbing it with a cloth).

    After many test we established that the problem was caused by the electrode topology. To explain this, here is a diagram of how the early prototypes looked:

    As can be seen, in electrical terms the circuit is a capacitor.
    This would not be an issue by itself, but we observed that the electrically charged objects only affected the detector when they were placed near the holes on the top of the metal box.
    Instead the problem is related to the alignment of the internal electric field with the (spurious) external electric influences.

    For the next revision, our ion chamber has been updated to use a positive electrode centred within the metal can:

    This way the electric field vectors are perpendicular to any electric noise that enters the chamber through the top holes, so theoretically the circuit would be more isolated.
    The new topology is also more similar to the rest of DIY ion chambers out there, and still can be manufactured with pick-and-place machines.

    Next updates will show the PCB design for the first hand-held prototype.

  • 5 - Correcting the effect of temperature

    Carlos Garcia Saura10/08/2017 at 23:20 0 comments

    The circuit we are using to measure radiation is derived from a DIY detector by Charles Wenzel: http://www.techlib.com/science/ion.html. It uses a high-gain Darlington transistor to amplify the tiny currents generated between the inner electrode and the outer shield.

    For our design we have chosen the FMMT734 transistor, an up-to-date part with standard SOT-23 surface mount footprint. We use the PNP configuration rather than the commonly used NPN; this way it is possible to have the outer shield at ground voltage.


    However in our first tests this circuit produced measurements that were very dependent on temperature. When temperature raises around the detector, the gain of the Darlington transistor is reduced and the output signal is substantially diminished.

    This is why the fourth iteration incorporates two transistors: one of them is connected to the electrode, and the other one is left open. The radiation measurement is then corrected by subtracting the reference output voltage from the signal coming from the main amplifier.

    Here are two pictures of the fourth prototype. The radiation sensor is the large metallic box, the rest of components are part of a plain old, boring IoT box (Internet of Things is soo 2016..).

    The fourth prototype was successful - there is a clear signal whenever the radiation source is put close to the detector. Also, the offset and the effect of temperature are removed by subtracting the reference signal from the unconnected reference transistor:

    The long-term test in a WiFi connected platform has also shown that the sensor is not capable of measuring the background radiation levels. Temperature changes over the course of hours and days, and this still has a notable effect that obfuscates any traces of low radiation levels (even after correcting with the reference transistor).

    However the sensor does produce a signal when radiation sources are close to the detector. We believe this sensor will be useful in a portable hand-held device that can be brought near objects to check if they are radioactive or not.

    Stay tuned for more updates, and tell us what you think! :-)

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Discussions

peter jansen wrote 11/11/2017 at 00:30 point

Hi Carlos,

This is an interesting project, and radiation sensing is definitely timely and socially useful.  I noticed that you didn't mention photodiode-based approaches in your introduction, which are very common and can be both reasonably sensitive and very low cost.  The wonderfully sensitive and versatile Radiation Watch Type 5 using the X100 is available at retail (e.g. Sparkfun, etc.) for about $70 ( https://www.sparkfun.com/products/14209 ).  For folks making their own, the BPW34S is very popular (Googling "BPW34S radiation detector" lists many existing designs), and some look to have their designs down to a few dollars (e.g. https://hackaday.com/2013/06/03/a-very-tiny-gamma-ray-detector/ ). I also used the popular Maxim appnote reference designs (e.g. https://www.maximintegrated.com/en/app-notes/index.mvp/id/2236 ) to put together an open source modular silicon PIN detector a few years ago that's about 10X less sensitive than the Type 5, but suitable for (super low resolution) imaging applications ( https://hackaday.io/project/5946-openct2/log/20074-assembling-and-characterizing-the-modular-detector-rev1 ), with a single-quantity BOM of about $30 (if I remember correctly).  Most of that was in a single op-amp (the preamplifier), the BPW34S photodiodes are only ~0.34 in quantity, so it's possible one could get the design to be much less expensive with a bit of refactoring to different opamps, and in quantity (and I think Alan Yates' design above pairs the BPW34S with a dual LM358 opamp, and Digikey is showing these as only 9 cents (!) in quantity -- really ultra low cost).  To demonstrate that your ~$17 design (or even a $10 or $5 design) is at least as useful as or better than the existing options in some application area, I think you would need to characterize it to show how sensitive it is to at least a few common low intensity check sources (since you mention that you're having difficulty detecting background radiation), and demonstrate some application that it's useful for. 

  Are you sure? yes | no

Carlos Garcia Saura wrote 11/14/2017 at 13:55 point

Hi Peter, thanks for your kind comment, I agree with everything you said!

I have not had the chance to work with semiconductor-based detectors, though in the first log entry I did link to a related project ( https://hackaday.io/project/1749-solid-state-ionising-radiation-detector ). I am not sure photodiode detectors are sensitive to alpha radiation.

Also, I will be taking steps to demonstrate the accuracy of this design. Indeed at the moment I do not have any quantitative results. Good thing is that I'm not reinventing the wheel: ion chambers are really good at what they do, so I'm quite confident on their sensitivity (specially to alpha radiation).

The next version of the Open Radiation Detector is going to use a very good op-amp to do the current amplification. Fortunately, with the Hackaday Prize lots of people has contacted me to try out the detector with Radon gas. So we are about to get some valuable data!

Finally, thank you for all your projects! I'm a big fan, specially of the open source tricorder :-)

Cheers!

  Are you sure? yes | no

Peter Camilleri wrote 10/29/2017 at 18:59 point

I wonder how sensitive this detector is to humidity. I mean, what happens if you breath on it?

  Are you sure? yes | no

Carlos Garcia Saura wrote 10/30/2017 at 22:57 point

Hi Peter! Indeed it is quite sensitive to humidity - if you breath on it the measured radiation output drops down. So definitely not to be used near liquids!

  Are you sure? yes | no

David Knochenhauer wrote 10/26/2017 at 06:39 point

Is it possible to measure background radiation with the new design? And can it be calibrated to throw out a value?

  Are you sure? yes | no

Carlos Garcia Saura wrote 10/26/2017 at 09:38 point

I don't think so, using the current electrometer circuit based on a darlington transistor. Gain still changes with temperature in the long term, even after compensating (see log entry 5). If we could figure out a way to amplify current that is accurate and independent from temperature, it would be possible to calibrate the device... I would really love to see this happen in the short term.

  Are you sure? yes | no

patricia pisonero wrote 10/21/2017 at 04:45 point

Thanks for sharing such an impressive project!

  Are you sure? yes | no

Carlos Garcia Saura wrote 10/16/2017 at 13:50 point

Thank you! I don't think it can detect radon with the same hand-held form factor, but Charles Wenzel has managed to detect Radon also with an ion chamber: http://www.techlib.com/science/ionchamber.htm I believe it would be very possible to create a similar radon detector with the PCB layout of my project. Cheers!

  Are you sure? yes | no

Domen wrote 10/15/2017 at 11:19 point

Will it be able to detect radon?

Otherwise great project and fantastic documentation!

  Are you sure? yes | no

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