THP Quarterfinalist: Low-Cost Solid State Cosmic Ray Observatory

There are a number of crowdsourced projects to put data from around the world onto the Internet, tracking everything from lightning to aircraft transponders. [aelias36]’s entry for The Hackaday Prize is a little different. He’s tracking cosmic rays, and hopes to turn his low-cost hardware into the largest observatory in the world.

Cosmic rays are protons and other atomic nuclei originating far outside the solar system. They hit the very top of Earth’s atmosphere at a significant fraction of the speed of light, and the surface of the Earth is frequently sprayed with particles resulting from cosmic rays. Detecting this particle spray is the basis for all Earth-based cosmic ray observatories, and [aelias] has figured out a cheap way to put detectors in every corner of the globe.

The solution is a simple PIN diode. An op-amp amplifies the tiny signal created in the diode into something a microcontroller can use. Adding a GPS module and an Ethernet connection, this simple detector can send time, position, and particle counts to a server, creating a huge observatory with crowdsourced data.

The detectors [aelias] is working on isn’t great as far as cosmic ray detectors go; the focus here is getting a lot of them out into the field and turning a huge quantity of data into quality data. It’s an interesting project, and the only one with this scale of crowdsourcing we’ve seen for The Hackaday Prize.

You can check out [aelias]’ entry video below.

SpaceWrencherThe project featured in this post is a semifinalist in The Hackaday Prize.

18 thoughts on “THP Quarterfinalist: Low-Cost Solid State Cosmic Ray Observatory

    1. At crazy high energies (EeV+), it’s useful because they’re produced extragalactically by unknown (and somehow crazy-efficient) accelerators, and the only way to figure out what those accelerators are is large statistics. There’s a small window in energy where cosmic rays could conceivable do particle astronomy, which would give a much stronger handle on the actual physical processes at compact sources.

      That being said you need much higher detector density to do this, and much bigger target mass to get actual useful results.

      Cosmic ray detectors don’t use the *photodetector* as the active collecting volume for the particles from the shower. They use either a huge amount of water (~10 tons per detector, times 1600 detectors for the Pierre Auger Observatory), producing light via Cherenkov radiaton, or a large amount of scintillator. And still in those cases the photodetectors are big (multiple-inch phototubes) since the light flux produced is still very low.

      The particle fluxes you’re trying to measure here are on the order of 0.1 per square meter. The chance of a flux of those particles hitting a PIN diode is zero. And then even if you tie it to some sort of light producer (scintillator, water) a PIN diode still won’t be good enough.

      1. I understood he is detecting the incident particles in order to map out the shower and estimate the point and angle where the original particle bombarded the atmosphere. You don’t need large scintillators or water for this, the atmosphere itself rains down electrons, gamma, muons etc. Not sure about the pin diode, but you can easily detect incident radiation with a Geiger-Muller tube.

        1. No, you misunderstand. The cosmic ray hitting the atmosphere produces gammas, electrons, and muons in an air shower, *but it produces them with a flux of about 0.1 per square meter* (at ~kilometer distances from the core).

          The flux near the core is much higher, but not high enough. Even if you assume the PIN diode is a square centimeter collecting area, that would require fluxes on the order of 10,000/square meter to see anything, and to see that you’d have to be within probably a few meters of the core.

          Which means you’d need all of the detectors packed less than 1 meter apart, which, if you want to instrument 100 square kilometers (so you see order 10/year above 10 EeV or so), means you need hundreds of millions of detectors.

          1. Also please don’t get me wrong: I’m not trying to discourage someone from trying to home-build an air-shower detector. Could you do it? Yeah, possibly. But you need big collecting area, even for a single detector, and then you want to put multiple of them at the same point to use coincident detection between them to kill noise. There’s a reason cosmic ray observatories have square-meter size collecting area instruments.

            I dunno – a large volume of water, lined with a UV reflective material, with some light sensor (maybe a cheap APD or PMT from eBay) might be able to detect small air showers. It’s tough to say what would win versus a whole bunch of muon detectors.

          2. Hmm, so a large number of Geiger tubes wouldn’t work? I’ve read about people detecting muons this way. I guess there is a large difference between picking up radiation, and picking up enough radiation to correlate and calculate useful information about the prime particle. Still a neat project though.

          3. A large number of Geiger tubes would work, sure. If each one is around 12″ long, and around 1″ wide, you’d need what, around 108 of them per detector to get up to a square meter. Even then the detector’s probably too small, and now you’re talking about over $1K in tubes.

            In terms of “cost per area”, water’s cheapest, but detecting Cherenkov light is hard. The Auger Observatory went crazy with three 9″ phototubes (at a kilobuck each), 10 tons of doubly-distilled water, index-matched optical coupling, and a highly reflective Tyvek liner, and that still only results in 300 electrons for a vertical incident muon. Scintillator light is easier to detect, but the detector is more expensive.

            Both the detector and the array just need to be big. Crudely, if you just wanted to detect air showers, and didn’t care about firmly establishing the size and characteristics of the shower, you could do it with 3 pairs of Geiger tubes, probably spread out around 100 meters apart or so. You would be absolutely *flooded* with low-energy showers, but this isn’t very far off from what people did back in the 50s or earlier.

            Would still be an interesting project, definitely. But you’re not going to get ~EeV showers – they’ll be primarily ~TeV/PeV showers, because there are billions more.

    2. “Observation of these cosmic rays is important/useful because???”

      Data helps us learn new stuff about our universe.

      But, for that mater, since when did a hack have to be important or useful ;)

      1. I used that Hamamatsu one, but detecting 20MeV. Unfortunately it’s export-restricted last time I checked because it’s used in some military system or other (I have no idea what). Expect a phone call asking what you plan to use it for before you can order any, a rather hefty duty charge, and a little paperwork (other than that no issue though). It’s a really nice part though.

        I had a hard time finding anything else that worked at room temperature. Many photodiodes are coated with thin glass coatings that kept blocking alphas.

        Fun fact: solar panels are huge PIN photodiodes. I’ve read at least one paper where they are used to detect high energy events, but I don’t recall at what luminosity.

        The radiation here is probably more penetrating than alphas, so perhaps a good strategy would be to take a small stack of monocrystalline solar panels, wrap it in very thin copper foil to act as both faraday cage and block ambient light. Also inside the faraday cage include an opamp at open-loop gain acting as a transimpedance amplifier… I like Burr Brown OPA132. The stack of panels is to give the detector some directionality; the detector cross section is better one way than the other.

        I was never able to get this working for alphas, but I only had polycrystalline panel handy, it was coated in thin glass which may have blocked them, and I only had a couple of days to devote to it.

        Good luck.

  1. PIN diodes can certainly be used for radiation detection of ionizing radiation, but there are better choices (for numerous reasons) for cosmic ray detection. A coincidence circuit is also needed to discriminate between terrestrial radiation sources versus those of cosmic origin. For a good write up of how to use dual geiger (GM) tubes (in coincidence), check out

  2. These diodes can be obtained from broken TVs and videos circa 1995 as a fair number used them as infrared detectors for the end sensor and remote.

    Once cast in opaque resin ie good old fashioned grey silicone for repairing car gaskets they should be just as efficient as the BPW32.

    Someone should totally make a few hundred of these and release them on balloons with little transmitters and dataloggers during a big solar flare to see how the radiation wave disperses :-)

  3. The QuarkNet program puts true cosmic ray muon detectors into the hands of high school students and teachers. The detector uses scintillator paddles, photomultiplier tubes, and a sophisticated coincidence detector to see, trigger, and log the passage of likely cosmic ray muons. Data is tagged with time from a GPS reference and uploaded to a central cluster for analysis and sharing. There are several hundred to a few thousand detectors in use worldwide.

    It seems this HaD project does not use local coincidence triggering, so the local node will see both electronic noise and false signals from terrestrial radiation. That will significantly increase the number of data points uploaded to the server, and puts the entire burden of signal discrimination on the post processing. Local coincidence triggering is done on very short time intervals in the QuarkNet detector, but in this HaD project would be dependent on the less precise comparison of station reported GPS signals. The pin diode also has a very small cross sectional area compared to scintillator or G-M tube detectors.

    I would welcome a lower cost solution to cosmic ray observing, but I would like to see a comparison of this gamma photon detector network to existing muon coincidence detector network observations.

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