Detecting Cosmic Rays With 18 Geiger Tubes

What do you do if you have 18 Geiger tubes lying around? [Robert] had an interesting idea to build a cosmic ray detector and hodoscope to observe the path cosmic rays take while flying through his lab.

[Robert]’s cosmic ray detector works by detecting the output 9 Geiger tubes on the y-axis and 9 Geiger tubes on the x-axis with a coincidence circuit. When a cosmic ray flies through the detector, it should trigger two tubes simultaneously. By graphing which of the two tubes were triggered on an array of 81 LEDs, [Robert] not only knows when a cosmic ray is detected, but where the cosmic ray was.

The detectors do pick up a little background radiation, but thanks to [Robert]’s coincidence circuit, he can be fairly certain that what he’s recording are actually high-energy cosmic rays.

Before building the 9×9 hodoscope, [Robert] built a similar drift hodoscope that simply plots the path a cosmic ray takes through an array of Geiger tubes. You can check out videos of both these cosmic ray detectors after the break.



21 thoughts on “Detecting Cosmic Rays With 18 Geiger Tubes

  1. Yeah, I wonder where people get such amounts of tubes cheaply.

    A quick look on eBay: 18x SI-22G or SBM-20 is still ~$360, shipping costs not included…

    Of course, you could still just pay up, even at $500 it’s still a nice setup. There are geiger counters on sale that are more expensive :)

    I would like to know if this can be done with the really cheap, deaf tubes like SI-3BG. They are far smaller but if you stack them precisely you could make a single pixel for detecting cosmic rays.

    1. Not really. The cosmic ray muon flux isn’t all that random: you get bunches in time due to high energy air showers (on scales of microseconds) and the total flux correlates with pressure (because of the change in air density).

      It probably wouldn’t be that bad, but you’d be better off just using ambient background radiation, I’m guessing.

      1. Actually, yes. Sort of. Radiation by itself is a poor source of randomness, but it’s a very good source of entropy. If you know what you’re doing (and there’s about a hundred different ways to mess it up that are very hard to test), you can use it as the input to a mixing or whitening function, or to seed a pseudorandom number generator.

  2. An instrumenting instrument, does it have any use in research, or is limited to displaying already known and understood phenomenon like an oscilloscope is often used for in the teaching environment, although an oscilloscope can be use fore research as well? Not that being a detector and display instrument for teaching isn’t good enough.

    1. This is a really interesting project, but it is not a hondoscope. You can only recover a position not a trajectory. It much more resembles a strip detector. However, is one could at least estimate the amount of background from the muson incidence and direction distributions.

    2. But, to get to your actualy question: As a non-hondoscope it would have use in research. In particle detectors it may be necessary to be able to remove cosmic muons from the measurements. Therefore you position muon detectors above and below the experiment. If you detect a muon in both, you know that whatever you saw in the actual detector was not from your experiment.

  3. I always thought a Hotoscope/hotograph portrayed the PATH of a particle, this displays where the path most strongly interacted a plus shaped array, but do not provide any details about the other points in its trajectory, I don’t believe this is a hotoscope, but rather just a detection array…

  4. I’d like to see a side by side video with the same setup in a commercial plane, to see how much difference there actually is in practice.

    Incidentally, this can’t touch the magic of a cloud chamber I have to say.

  5. Yes it is not exactly a hodoscope (need more layers and software) more a work in progress. This is apart of a group of projects I’ve been building over-time and not really intended to achieve any significant scientific outcome (not sure hack-a-day is that kind of spaCe anyway). This is about having fun, learning and hopefully creating interesting displays that clearly demonstrate the natural radiation that results from interstellar high energy particles which are all around us and pass through us everyday.

    I started out a few years ago thinking it wouldn’t be hard to make and although this project is relatively easy on a per channel basis their are many failed prototypes behind them. Still more to come ;-)

  6. Very cool! I’m wondering, do the cosmic rays stop when they hit the detector?

    I have a hunch that they don’t and that may explain how sometimes three or four LEDs in a row (random direction) light up simultaneously… pretty cool stuff!

    1. In general, they do not. They will just lose some energy. They may however decay somwhere in the setup, for example in the electronics box below the detector. This would result in an electron, which then could also be detected (and two neutrinos, which would be a really cool project to detect them at home ;) ). But without a set of lead blocks below the device, this is quite improbable, so nothing you would see more than once an hour.

      Also, that one muon hits several pixels on the hondoscope simultaneously would require it to follow a trajectory with a very high incident angle. The distribution function for cosmic muons however is proportional to cos^2, which results in a probability like this:^2(x)%2C+-pi(1%2F2+-+1%2F16)%2C+-pi(1%2F2-2%2F16))%2Fintegrate(cos^2(x)%2C+pi*(1%2F2)%2C+-pi*(1%2F2))

      You may have some fun playing around with the incident angle range (the boundaries for the first integration), but I don’t think that this may give you values that are much higher, as long as the incident angles make sense. ;)

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