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Homework Help: Some questions about Spectrum Techniques Lab

  1. Dec 7, 2014 #1
    1. The problem statement, all variables and given/known data
    i have some questions and some of them i cant answer. The questions are form the
    "Spectrum Techniques Lab Manual Student Version"

    the link for this manual https://www.google.com/url?sa=t&rct...=fpanN3GAbmQv5T4gH_qn-Q&bvm=bv.80642063,d.d24

    Lab #1: Plotting a GM Plateau

    1. Read the introduction section on GM tube operation. How does electric potential effect a GM tube’s operation?

    If we increase the electric potential more positive ions and negative electrons will be accelerated to the cathode and anode

    2. Will this value (the operating voltage of GM tube) be the same for all the different tubes in the lab?

    No it will not because of difference in their construction

    3. Will this value (the operating voltage of GM tube) be the same for this tube ten years from now?

    No it will not because the gas permanently break down over time ( life time)

    Lab #3: Background

    1. Name the four natural sources and three man-made sources of background radiation.

    Natural sources: Terrestrial Radiation,Cosmic Radiation, Cosmo genic Radiation
    Man-Made Sources: Nuclear reactors and weapons

    2. Is there any way to eliminate background radiation?

    Radiation has always been present in the environment and in our bodies. Therefore it is impossible to eliminate Background Radiation.

    3. Are all the background measurements exactly the same number of counts? Is there a systematic cause for this?


    Lab #5: Geiger Tube Efficiency

    1. How can you determine the activity of a radioactive source?

    By using the equation

    ## \%E=\frac{r(100)}{CKG} ##


    r= is the measured activity in cpm minus the background radiation rate

    C=is the expected activity of the source in µCi

    K=the conversion factor (convert from dpm to Ci) 1Ci=2.22*1012dpm

    G= the fraction of the emitted radiation

    2. Do you expect efficiency to be good or bad for each of your sources? (Consider real-world effects)

    The efficiency is related to the kind of radiation (α, β, γ). The best efficiency is get by using gamma particles.

    3. Is the efficiency you calculated for each isotope valid only for that isotope? Explain your answer.

    The efficiency varies with the type of incident radiation

    Alpha particles are not particularly energetic—their source must be kept close to the end window of the G‐M tube, or they will be stopped in a short distance in air. Gamma radiation, itself, has a small probability of ionizing the gas in the G‐M tube because it is detected essentially when it scatters electrons in the metal cylinder surrounding the gas into the tube.

    Beta particles that enter the tube have the largest odds of ionizing the gas in the tube.

    As a result of these facts, a G‐M tube tends to be much more efficient for detecting beta particles

    4. If a different shelf is used, will the efficiency change? Explain your answer.

    The efficiency will change since the distance will change and because of the equation

    ## \%E=\frac{r(100)}{CKG} ##


    ##G=\frac{1}{2} - \frac{d}{2\sqrt{x^2+d^2}}##

    d is the distance ( shelf used)

    Therefore if d gets bigger the efficiency will be smaller and vice-versa

    5. (Correlates if five minute and one minute runs were taken.) Are the Efficiencies different? How different? Why?


    Lab #8: Inverse Square Law

    1. Write a general mathematical expression for an inverse square law.

    ##I=\frac{C}{4 pi R^2}##

    2. What are other examples of inverse square laws?

    Inverse Square Law, Gravity

    Inverse Square Law, Electric
  2. jcsd
  3. Dec 7, 2014 #2


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    Gold Member

    Ok, first off, no one is going to read 123 pages of pdf. That's just too much. Nothing you said really jumped out as me as problematic, but this is not my area of expertise.
    look up dark counts w.r.t. entanglement. I believe this is the same fundamental concept that's being asked about i.e. "noise".

    look up boxcar average on google.
    Here's one link I skimmed through, seems useful enough.

    again, these things aren't necessarily specific to your geiger tube, but these problems occur in various areas of physics, and there are ways to deal with them.
  4. Dec 7, 2014 #3
    Thank you for your answers.
    but I don't want you to read this pdf. I just shared so as other people who already read this pdf will remember it and maybe answer my questions or correct my answers.
    I thought some user will have enough information to correct my answers if they are wrong
  5. Dec 7, 2014 #4


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    Gold Member

    No problem.

    It seems as though you're diving into the realm of the so called real world, with noise, and a significant lack of frictionless surfaces. (the guy at the hardware store laughed at me when I tried to buy one)

    So you have some data, that you got from a REAL experiment. That means that your signal no longer looks like ##e^{\gamma t}## but instead looks like ##e^{\gamma t} + f(noise,noise, \text{why not?} \ more \ noise)##

    How can you get rid of said noise? (Or how can you separate that noise from your "good data")
  6. Dec 7, 2014 #5
    Ok thank you. I got it
    I made the experiment on 4 different GM counters and got 4 different average value for the background radiation.
    I thought the reason is that some of the radiation wont enter the GM tube at specific time.
    And at another time they will enter because of the geometric construction for each GM counter.

    Do you think my answers for the other questions are correct?
  7. Dec 7, 2014 #6


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    Gold Member

    Most seems fine to me other than a slight lack of detail and im not counting the same number of "resources" as whats askd.
  8. Dec 7, 2014 #7
    Ok thank you very much for your help
    I will keep searching for more information and maybe i can make my answers better.
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