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Radioactivity - Why no reading on Geiger counter?

  1. Apr 29, 2008 #1
    [SOLVED] Radioactivity -- Why no reading on Geiger counter?

    1. The problem statement, all variables and given/known data

    A magnet is directly between a Geiger counter and a material that is know to be radioactive. If the Geiger counter does not register any radioactivity, what kinds of particles is the radioactive substance emitting?
    Why doesn't the Geiger counter register any radioactivity?


    2. The attempt at a solution

    What kind of particles? Either one of the three: Alpha, Beta, or Gamma.
    We can't say for certain because the magnet will definitely stop alpha and beta particles. Now since the Geiger counter doesn't register any radioactivity, ....

    *Kinda stuck.*

    Let's answer the 2nd question first.

    The Geiger counter doesn't register any radioactivity because the magnet placed in between the counter and the radioactive substance is evidently stopping the radioactive particles.

    Then now to the first question.....

    We cannot say for certain which of the three radioactive particles is being emitted by the substance because the magnet will definitely stop alpha and beta particles. Now since the Geiger counter is not registering any radioactivity, it's also possible that gamma rays were stopped by the magnet.



    Now where I need your opinion...
    Does my answer make sense? Is this question really that simple to answer?

    Do you think that the magnet can stop gamma rays? Because if it cannot, then the substance is not emitting gamma rays, because if it were, then the rays would have passed through the magnet and cause a reading on the Geiger counter.

    PLEASE HELP!!!


    Thank you!!!
     
    Last edited: Apr 29, 2008
  2. jcsd
  3. Apr 29, 2008 #2
    Ask yourself, what physically are Alpha and Beta radiation emitters and how would a magnetic field affect them? Then ask yourself whether this would affect gamma radiation (photons) for the same reason.
     
  4. Apr 29, 2008 #3
    Gamma Radiation has no charge, so the magnet will have no effect. Gamma emission does not have to have a long range, I know in the lab I have dealt with Gamma Radiation (Cobalt-60) that could only be detected within 30 centremetres!!

    As far as I am aware there are three ways to detect for Gamma Radiation excluding Alpha and Beta. One way is to use a magnet as you have suggested, gamma rays are not effected to go straight through, while alpha and beta are attracted to each side of the magnet. The second is purely by using distance, Gamma Radiation has the longest range, so in some cases you can just have a large distance. The final way that I know if is to put a sheet of aluminium between the source and the GM counter, this sometimes absorbs the alpha and beta particles, though this way is hard to know when all the alpha and beta particles are not going through. I would say go for the magnet, if that doesnt work, then distance. And if that doesn't work them I have no idea. I will be interested to see what other people would do!

    Your GM counter should be picking something up, I usually get a background count, that is where there is no source present.

    Hope this helped! If anything remember that Gamma Radiation has no charge!

    _Mayday_
     
  5. Apr 29, 2008 #4
    Or there's your answer.
     
  6. Apr 29, 2008 #5
    Haha! I didn't know how much detail to go into, I mean it's not really something you can work at, it probably more a case of knowledge. I hope i have still obeyed the Homework Help forum guidelines!
     
  7. Apr 29, 2008 #6
    Hmm...

    It's a good thing I posted this problem here and asked for a second (and third) opinion!!

    Thanks to you two, astrorob and Mayday, I went back to my textbook... And I found out that the magnet does have a purpose in radiation!!!

    Like I said in my first post, I thought the magnet's purpose was to stop the radiation. But now I know that the magnetic field actually separates the three radioactive particles!

    So now with this new factor.......

    wait let me post this first to see if there's a new post.
     
  8. Apr 29, 2008 #7
    Well a magnet would have, but that would just be to steer the alpha and beta particles away from the GM counter.
     
  9. Apr 29, 2008 #8
    According to the illustration in my textbook, gamma rays would have continued in the same direction after the passing through the magnetic field. Alpha and Beta particles traveled in opposite directions.

    So in answering the question.... What particles was it emitting? -- It was not emitting gamma rays because if it did, the gamma rays should have passed through the magnetic field and registered on the GM counter. But since it didn't, that means that the substance was either emitting Alpha or Beta particles.
     
    Last edited: Apr 29, 2008
  10. Apr 29, 2008 #9
    Then the second question.....

    The GM counter did not register any radioactivity because the two possible particles that the substance was emitting were steered away from the counter by the magnetic field.
     
  11. Apr 29, 2008 #10
    Okay, well if what you have said is correct, then there is no Gamma Radiation to take into consideration. Beta particles will move further in air than alpha particles. Maybe try having a look at a Bubble Chamber, of Cloud chamber. Those work in relation to how ionizing the particles are.


    Yes, that is highly probable.
     
  12. Apr 29, 2008 #11
    What would your answer be to why the Geiger counter did not register any radiation?
     
  13. Apr 29, 2008 #12
    (sorry if the question seems like I'm challenging you... hehe)

    I'm not!!!
     
  14. Apr 29, 2008 #13
    The GM counter should detect a backgrounf count. If not, then you would say that no radioactive emission was present, as nothing was detected.
     
  15. Apr 29, 2008 #14
    Mhmm....

    well my textbook only talks about the Geiger counter in a caption for a picture. It didn't discuss exactly how it works.... So I don't know much about it.

    But according to the problem.. The counter did not detect anything! And so I'm supposed to explain WHY...

    Oh well. I've actually had a number of complaints on these Physics exams made by American School... But the textbook is great! (Paul G. Hewitt's Conceptual Physics)

    Anyway... Thank you very much for your help!!! (and thanks to astrorob also =))
     
  16. Apr 29, 2008 #15
    Post the question! Or have you already done so? If there is no reading on the GM counter, then there is no radioactive emission in the space being measured.
     
  17. Apr 29, 2008 #16
    The question?

    It's on my first post on the top of this page.

    Here it is again:
    A magnet is directly between a Geiger counter and a material that is know to be radioactive.
    If the Geiger counter does not register any radioactivity, what kinds of particles is the radioactive substance emitting?
    Why doesn't the Geiger counter register any radioactivity?
     
  18. Apr 29, 2008 #17
    The particles would be those that are charged (Alpha and Beta) the geiger does not register as the alpha and beta are attratced to the magnet, and it is possible that there is no gamma emission.
     
  19. Apr 29, 2008 #18
    Magnet illustration = please look at, _Mayday_

    Here's the illustration in my textbook. Please click on the image: Magnet.jpg

    I'm basically imagining now that the Geiger counter is above the magnet. It should then be getting gamma radiation... But since the question is saying it's not, then does that mean the substance is not emitting gamma rays?
     

    Attached Files:

  20. Apr 29, 2008 #19
    It means that the substance is emitting high energy gamma rays. Low energy photons can be detected by some geiger counters, but most high energy photons will pass through unhindered.

    As for the alpha and beta emitters, these are charged particles, deflected by the magnetic field away from the counter.
     
  21. Apr 30, 2008 #20
    Okay... I confirmed what you said, astrorob... and so how about this as my answer:

    Again, the first question is, if the Geiger counter is not registering any radioactivity, what kinds of particles is the radioactive substance emitting?

    Answer: The substance may be emitting one, two, or all three particles, which are the alpha rays, beta rays, and gamma rays.


    2nd Question: Why doesn't the Geiger counter register any radioactivity?

    Answer: The counter does not register any radioactivity because the magnet placed between the substance and the counter will deflect any alpha and/or beta rays and steer them away from the counter. What about gamma rays? Well, it is possible that the substance is not emitting gamma rays. Another reason is because high energy gamma rays can pass through the counter undetected.
     
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