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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.

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 built upon a standard shield that is commonly used to protect circuits from interference. It incorporates a 12V battery and a transistor amplifier circuit with a buzzer that alerts 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 design
  10. It works!
  11. Sources are available! Next steps

Also check out the GitHub page below.

Project sources

All the designs are freely available in GitHub (https://github.com/CarlosGS/open-radiation-detector...

Read more »

BOM_open_rad_detector_0.9.pdf

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

Adobe Portable Document Format - 40.40 kB - 10/17/2017 at 09:54

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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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  • 11 - Sources are available! Next steps

    Carlos Garcia Saura2 days ago 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 Saura3 days ago 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 Saura4 days ago 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 Saura7 days ago 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, which drops down the resistance of the reference voltage. We have done this to guarantee that the radiation signal is always greater than the reference signal. 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. Removing R5 could otherwise inhibit radiation detections in some circumstances.

    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! :-)

  • 4 - Ionization chamber prototypes

    Carlos Garcia Saura10/08/2017 at 11:06 0 comments

    Spark detectors, as well as Geiger counters, require of very high voltages to operate. These must be avoided in order to achieve a simple detector circuit. Dropping the requirement for a high voltage would be more safe and need less power to operate.

    Ionization chambers are the solution to this problem. Rather than generating sparks or discharge pulses, they use a low voltage to separate the ions created when high energy particles interact with a gas (air, in our case). These tiny ion currents are then measured with a very simple amplifier circuit.

    There is a long history of detectors based on ion chambers. They have already been used in professional radiation monitoring equipment, and moreover, many hobbyists have come up with very simple designs that can be built at home. Check out this website to learn more about DIY ion chamber radiation detectors: http://www.techlib.com/science/ion.html

    The simplicity and high sensitivity of ion chamber detectors makes them ideally suited for this project.

    Our first iteration used the same layout as the "spark detector attempt" we showed in log entry 3.

    Instead of applying a high voltage that causes sparks, using it as a ionization chamber means we applied a low potential (12V) and measured the tiny ion currents induced by radiation.

    This design did NOT work because there is only a tiny volume of air between the electrodes, and plenty of leakage between the "finger plates" as contact surfaces are large.

    The second iteration started as a very ugly prototype that we are not going to mention again:

    Let's focus on the "pretty" prototypes instead.

    The idea behind the new design is as follows:

    An electric field is created between the electrode plate and the outer case. The ionized air is attracted by the electrodes, and a current can be measured. These ion-induced currents are proportional to the amount of radiation present.

    The interesting thing about this approach is that it uses a printed circuit board as part of the sensing element. This is the key to reduce manufacture costs.

    The third iteration was built with a commercially available circuit shield. It also incorporated a ground plane behind the electrode to reduce the effect of static electricity over the measurement.

    This prototype actually worked!!

    Bringing a radiation source near the detector generated a voltage on the multimeter:

    The first success was very rewarding - it proved that we were on the right track!

    For the next log entry we will review the amplifier circuit and the long term effect of temperature in the detector.

    If you like this project, be sure to click the follow button to not miss any updates!

  • 3 - First attempts: an alpha spark detector

    Carlos Garcia Saura10/04/2017 at 17:21 0 comments

    Today I want to share my first attempt at building a spark particle detector.

    Spark detectors consist on a strip of wires parallel to a high voltage plane. A strong electric field is created, and every time a high energy particle ionizes the air between the electrodes, it causes an avalanche effect and a spark appears.

    From my ignorance as a novice in the field, I initially thought that the most important part of spark detectors were the parallel cables. So I went ahead and designed a circuit board with a "finger electrode" with a flat arrangement. A prototype was quickly made using a Cyclone PCB Factory:


    The next video shows the ""spark detector"" in action. The high voltage was generated using the flyback circuit from a document scanner, and was fed into the electrode through a protection resistance of several megohms.

    First time on, the circuit was already creating very promising spikes!

    Unfortunately, it was too good to be true. The sparks observed were NOT due to background radiation. This became evident after bringing a radiation source (from a smoke sensor) near the detector and seeing no change in activity at all.

    Among the many reasons for failure were the small and non-homogeneous electric field and tiny ionization volume. The randomness of the sparks seems to arise from local changes in humidity: every time a spark occurs, it dries the air around it and reduces the chance of a spark happening in the same spot.

    So this prototype was left behind as an anecdotal, tiny light show. In the next updates we will show the newer designs that actually work as a radiation detector. Be sure to follow the project to stay tuned.

    And thanks for reading! Have you ever tinkered with spark particle detectors? Share your experience and comments below!

  • 2 - The background: lots of DIY projects

    Carlos Garcia Saura10/03/2017 at 09:13 0 comments

    I've been there: you've just read that article about the potential danger of some household items being radioactive. You now have a strong need to check your granite countertops, camera lenses, smoke detectors and every weird-color dishes at home - for the sake of safety of course (note: these are very rarely an actual threat).

    You quickly find out that radiation detectors are surprisingly expensive. The only affordable options are labeled as "electromagnetic detectors" and don't really measure the harmful ionizing radiation that we want to check for.

    As a a maker yourself, avid reader of Hackaday, you go for the next logical option which is to build your own detector. A quick search yields lots of weird and wonderful projects:

    You quickly reach the most important page on the subject: a very detailed explanation by Charles Wenzel with a tutorial on how to build your own "ionization chamber" using a tin can, a transistor and a multimeter.

    These home made detectors are very cool, and a really nice option if you have the ability and free time to build them. In my case, I spent some time building a DIY detector and actually struggled during the way: it was very difficult to get consistent results. Every tin can was different from the one in the tutorial, the transistors required were not available at any store, the multimeter had too low internal resistance, lots of leakage, then the sensor was affected by static electricity, etc.

    It was after being bit by all of these variables, I decided to go ahead and design my own detector. It had to be built only from standard components. No more messing around with recycled tin cans, vintage transistors or cold-war vacuum tubes.

    Thanks for reading! Follow this project to get notified of the next updates.

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Carlos Garcia Saura wrote 2 days ago 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 3 days ago point

Will it be able to detect radon?

Otherwise great project and fantastic documentation!

  Are you sure? yes | no

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