Cosmic Ray Detector

When high energy radiation strikes the Earth from space, it’s called cosmic rays. To be accurate, a cosmic ray is not like a ray of sunshine, but rather is a super-fast particle slinging through space. Think of throwing a grain of sand at a 100 mph… and that’s what we call a ‘cosmic ray’. Build your own electroscope with this video!

Please login or register to read the rest of this content.


50 Responses to “Cosmic Ray Detector”
  1. catherine_pruitt says:

    Ok thanks

  2. Aurora says:

    Which part are you having trouble with?

    I can take a video and show it working – not sure why I didn’t do that in the video! Sorry about that.

    You’ll have the best luck with static electricity experiments on days that are warm and dry. If it’s raining outside, it’s not going to work (the water moisture in the air discharges any static build-up). The only other thing that can go wrong is that the mental rod you use is wrapped in insulation or the foil leaves are crimped together and not able to fly apart. Feel free to show me your setup ([email protected]) so I can see what’s going on with your experiment so I can help!

  3. catherine_pruitt says:

    We can’t do it can you show it in a video next time?

  4. Aurora says:

    I am not sure what you are thinking – can you please try again so I can answer your question better?

  5. Tyler says:

    Why can’t you just take off the tinfoil on top of the wire and leave it by itself and touch the wire?/:( it never made sense why.

  6. Aurora says:

    Hmm, if you can’t see the vapor trails and you only see the mist or smoke, wait another 10 minutes for your system to get really cold. Put your hand on top of the jar to warm it (the side without the dry ice). Did you also turn off the room lights and use a flashlight to shine the beam through the side of the jar? If after waiting still no tracks appear, check to be sure you have an airtight seal. If not, tighten that lid and try again, and you can even add a little more alcohol first. You can also change the position of the jar – sometimes it’s hard to see the tracks in certain positions, so you can place black paper behind the jar so it’s not quite so see-through. If all those tricks don’t help, I would use a larger jar and a different radiation source. Hope this helps!

    (For those of you wondering which experiment we’re talking about – it’s the “Alpha Particle Detector” in Unit 7)

  7. Jennifer says:

    Hi, we’re trying to do the cosmic ray detector with alcohol and dry ice. Followed to the letter as far as I can tell but didn’t work – no trails at all. Please give some tips to increase the probability of this thing working. Thanks. Jennifer

  8. Aurora says:

    You need something small and lightweight for the leaves so they can move with the lightest charge.

  9. Melanie Williamson says:

    does any metal work?

  10. Aurora says:

    Hi Andie! Just one – you need a bare piece of metal to stick through the lid and hold the foil in place. If you use a wire coathanger, be sure to strip off the insulation first, especially if it’s clear!

  11. Robert D'Angelo says:

    Hey Aurora, it’s Andie. I was wondering, how many wire coat hangers do you have to have?

  12. Aurora says:

    I am having trouble understanding your message. Can you be more specific about what the experiment is or isn’t doing? You can even send me a photo or a video so I understand better what’s going on.. it’s hard to figure out when I am not right there next to you. Please let me know how I can help.

  13. Renu Goel says:

    ms arora,

    we followed all the instux but it does not work, does it not work with a meatal lid

  14. Aurora says:

    A metal lid might dissipate the charge so it won’t build up, but you should still be able to see the leaves stretch apart. Is it humid today where you are? If so, this experiment will not work until the air dries up more.

  15. Beckye Frey says:

    We tried several times with balloons and socks, but nothing worked.
    Is having a metal lid a bad thing?

  16. Aurora says:

    No, magnetic POLES are totally different from an electric CHARGE. Like charges: plus and plus or a minus and minus will repel each other. Like poles also repel: north and a north side of a magnet will exert a push on each other, for example. The charge on the foil is the same on both halves, so since they are the same, they repel and exert a push on each other. You can either charge the foil with positive or negative charges, depending what you rub and with what.

    Human hair tends to give away electrons and become positively charged, so when you touch the ball of the electroscope to your head (after you rub the balloon with it), the foil will be positively charged. If you touch the balloon to it instead (after rubbing it on your head), the will foil be negatively charged.

  17. Gabriele Pealer says:

    Why do the two tinfoil flaps open up away from each other when charged? Does it have to do with the north and south ends of a magnet?

  18. Aurora says:

    This is an electroscope, which is how you can detect beta decay (electrons) in the atmosphere. It’s also something you can use to detect static electricity. I use these in class to teach kids about static charge before we move onto current through a wire, so they understand it’s really the same thing. If it’s not your thing, you can just skip it to move onto something that excites your interest more. 🙂 There’s plenty to choose from!

  19. Michelle Palmer says:


    Im trying to figure out why we would need this? Is it anything we could use for practical purposes? Why do scientist use these? What are they used for?

  20. Aurora says:

    Not magnetized (that’s North-South, like a magnet), but charged (plus-minus). Touch the top ball and it should reset. If not, unscrew the top and curl them away from each other slightly.

  21. Jennifer Lengyel says:

    Um my aluminum leaves maybe got magnetized or something, because one side attracts each other and one side repulses each other. Is there anything I can do?

  22. Aurora says:

    Yes – here they are:

    1. How does this detector work? (When the particle enters the chamber, it smacks into the alcohol vapor and makes free ions. The vapor in the chamber condenses around these ions, forming little droplets which form the cloud trail.)
    2. Do all particles leave the same trail? (No. Different types of particles leave different trails. Alpha particles are heavy and create straight, thick trails. Beta particles, which are light, will leave light, wispy, trails. If you see any curly trails or straight paths that take a sharp turn, those are particles that have smacked into each other.)
    3. What happens when the magnet is brought close to the jar? (You can use a magnet to deflect the cosmic rays if the magnet is strong enough and positioned just right.)

  23. Suna Price says:

    Are there answers to the worksheet exercises for this experiment?

  24. Aurora says:

    You’re right – the video is the wrong one! So sorry about that. We’ve been updated the players any I think my programmer mixed this one up.
    I’ve updated it so it’s the correct video now.

  25. Michelle Petersen says:

    The video shows detecting particles using a fog chamber with dry ice, isopropyl alcohol and a jar with felt. Is this the correct video to go with the electroscope handouts?

  26. Aurora says:

    It sounds like the experiment worked based on your comments here! The foil flaps moved when you brought the balloon next to the foil ball (that’s what is meant by “charging” it… sorry for any confusion around that!)

    Discharging means that you touch it with your finger to “ground” the device, which means that there are now not a positive or negative charge on the ball (and also foil strips) so they hang down. When you charge it, you are usually adding more electrons to the ball, and it sounds like the balloon worked the best for you. If you have access to an old CRT TV (the kind of TV with a curved screen), those work REALLY well. We’ve had kids report they’ve slid down a plastic slide with it, brought it near the dryer, and other fun things like this to “detect” large areas of static electricity. 🙂 Hope this helps!

  27. Rachelle McGuire says:

    We did this experiment the other day. Let me tell you what we did so you can tell me where we went wrong. We used a large canning jar covered with a piece of paper cut out to fit over the jar, then instead of using a hanger we used 2 small paper-clips twisted tightly together. We then followed the other directions exactly. The foil flaps did, indead, slightly fly apart from each other when the balloon got near the foil.So we knew that it was working. However, after that, the foil simply went back to its original position and did not move againlike the video suggests. We wondered if perhaps we did not understand what it meant to “charge” the device? And I thought perhaps using 2 paper clips was causing it to not work well so we tried using one but that didn’t work at all because it was too top heavy with the foil. So then I decided that we should use a wire hanger (we shaved off all the coating) and made it again. This time we still used paper to cover the jar but we hot glued the hanger in. It worked even worse – the flaps just barely barely moved when we brought the balloon near. It was not humid. Both times, with the paper clip and the hanger, the only thing that even slightly worked was rubbing the balloon on our heads – nothing else that we tried would charge it. Guesses as to what we can change to make it work? Also, the exercise questions were confusing. We had no idea what kinds of other things to do to charge it, and you did not explain what “discharging” meant. There was also a question about magnets but neither the video nor the written instructions mention a magnet. I found this, our first experiment, to be confusing and disappointing.

  28. Aurora says:

    Yes, discharging means grounded, and you can do this just by touching the foil ball on the top. The all is constantly being hit by charged particles all the time, so you’ll see the foil leaves twitch a bit every 5 to 10 seconds (as long as it’s not too humid or raining). If you rub a balloon on your hair and then bring it close to the ball and you’ll see the leaves move far apart!

  29. Nima Foell says:

    How do we discharge the electroscope? how do we ground it? does grounding mean discharging?

  30. Aurora says:

    Hmm… I am not sure without seeing your experiment in person. Make sure it’s not humid (you’ll want to do this on a warm, dry day) and that the ball is touching the metal rod and the rod is touching the foil strips inside the jar. You shouldn’t have tape between them or it’ll act like an insulator.

  31. Aurora says:

    There are lots of ways! You can rub a balloon on your head and bring it near the top conductor. 🙂

  32. Walter Rodriguez says:

    how do you charge your electroscope?

  33. Carole Wildes says:

    My electroscope does not work very well. I cant see the parting. Is there a size that the ball needs to be or is the tape a problem? Thanks.

  34. Aurora says:

    Whoop! That’s the wrong video… I’ll get that fixed in a jiffy. It looks like this one got mixed yo when we upgraded our experiments. Sorry about that!

  35. Margarita Fountain says:

    Hi, I was on the cosmic ray detector page, and I first watched the video, then I opened up the worksheet, but then I noticed that the worksheet and the video are two different things. They are bot labeled ‘Cosmic Ray Detector’, but the worksheet has a bunch of stuff in the materials section that are not in the video, or the instructions. I didn’t read any furthur than that, but they had for example, magnets, rubbing alcohol, heavy gloves, dry ice, none of these things were in the video or the instructions. Do you have a seperate video for it maybe? Any different instructions for the electroscope? Please reply,

  36. Lillian Jackson says:

    this looks fun and I’ll have to try it sometime!

  37. Aurora says:

    Did you get my email about the encore teleclass? We had so many folks excited about the class but missed it that we’re doing it again in a couple days.

    And yes, we’re turning the class into a video and posting it to the site – you’ll see it listed under ‘Latest News’ on the main page when it’s up next week.

  38. Caroline Wood says:

    I missed the teleclass today. Would it be here somewhere?

  39. Aurora says:

    Yes, look in Lesson 3 – it’s all about relativity.

  40. Hope Martin says:

    Oh, and are there any special relativity experiments to try? because the Relativity thing kinda fried my brain….

  41. Hope Martin says:

    Oh, okay~ thanks Aurora! It’s funny; I actually already used a ballon that i found.

  42. Aurora says:

    This is a very tricky experiment, meaning that it’s super-sensitive and easy to over-load so you don’t see the charge. The first challenge is to get the electroscope to work and detect static fields – be sure you can get the foil leaves to flicker and move when you bring it near a static field (like a charged balloon: charge a regular latex balloon by rubbing it on your hair for a minute. It will now have a negative charge.).

    Once you’ve verified this works, set the electroscope in a space that’s clear of metal (i.e. don’t put it on the dryer). Outside in the sun is a good choice. Leave it for a minute so it will settle, and then watch for tiny movements with the tinfoil. If you’re in a good spot, you’ll see the foil twitch very slightly as tiny charged particles whack into the metal ball on top. These particles carry a *tiny* amount of charge compared to your hair-rubbed balloon, so be patient!

  43. Hope Martin says:

    (i’m not really Hope, i’m her son ^^;)

    so i got the electroscope part to work, but i didn’t see any flickering. And by “charged”, do you mean holding the staticky surface next to the wad of tinfoil for an extended amount of time? or is it “charged” when you hear the static make it’s way to the receiver?

  44. Sophia Poli says:

    dose the jar have to be glass????

  45. Aurora says:

    This one is very tricky – see notes in the project and find someone who’s got a keen eye and a lot of patience.

  46. Tricia Sickmeier says:

    didn’t work, maybe we didn’t sand enough.

  47. sevy keble says:

    OOOOO! thats a really good idea! I might try that!

  48. Aurora says:

    You can use any piece of wire you have. Make a mini one out of a large paper clip, perhaps?

  49. sevy keble says:

    Aw, to bad we couldn’t do this! We ran out of wire coat hangers. 🙁
    sevy keble 🙂

Have a question?

Tell us what you're thinking...

You must be logged in to post a comment.