1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Determine type of particle emitted from decay?

  1. Aug 30, 2015 #1
    1. The problem statement, all variables and given/known data
    A Phosphorous 34 decays and emits a particle. A JJ Thomson experiment is done to find out the charge to mass ratio of this particle. The particle moves undeflected through mutually perpendicular magnetic and electric fields of 2.00 x 10-3 T and 1.08 x 104 N/C, respectively. When the electric field is turned off, the particle deflects to a radius of 1.53x10-2m. Determine the type of particle emitted.
    2. Relevant equations
    Fe = electric Force
    Fm = Magnetic Force
    Fc= centripetal Force
    B=Magnetic Field
    r=radius of curvature
    m=mass
    v=velocity
    E=Electric Field
    q=charge of particle

    Fe= qE
    Fm=qvB
    Fc=mv2/r

    When the electric field is turned off we know that Fm=Fc
    Because the particle is undeflected, we know that Fe=Fm



    3. The attempt at a solution
    To find the v of this particle, we can manipulate the formual of Fe=Fm into:
    E=vB
    v=(E/B)

    To find the mass of the particle we can manipulate the formual of Fm=Fc into:
    m= (Fc x r)/v2

    So, i figured out the velocity and mass of the particle, and now I am trying to determine the type of particle emitted. Am i able to do this using mass only? Or should I try and find the charge of the particle, and if so how?

    Thanks
     
  2. jcsd
  3. Aug 30, 2015 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You have no info to help you find the charge. So you are restricted to the type of particle (pion, muon, Kaon, electron/positron), just like the exercise text puts it.
     
  4. Aug 30, 2015 #3
    Would i be able to manipulate Fm=Fc to find q (the charge).
    qvB=mv2/r
    q=(mv)/(rB)
    ?
     
  5. Aug 30, 2015 #4

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If you have the direction of ##\vec B##, ##\vec v## and know which way it deflects, yes. But you don't.
     
  6. Aug 30, 2015 #5
    Alright. I figure the charge to mass ratio should be:
    Fm=Fc
    qvB = (mv2)/r
    (q/m)=v/(Br)
    When i crunch the numbers I get an answer of 1.7647 x 10 11
    Same as an electron..what do you think of this?
     
  7. Aug 30, 2015 #6

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Crunching numbers gives a number. But you need a mass. In kilograms, preferably (not in stones, lbs or that kind of stuff).

    Pretty heavy electrons ! perhaps ##10^{-11}## (if the 'number' is in kilograms) ?

    :wink:

    But I think you are doing fine. Click 34P in this table to see the decay mode...


    [edit] Oops I forgot, ##m_e = 9.10938291 × 10^{-31}## kilograms ?!?!

    [edit] Oops2 I remember the value of e/m in C/kg is the same as your number, that's a lot better !
     
  8. Aug 30, 2015 #7

    Sorry I should have included the units in my ratio. Awesome. Thank you for the help.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Determine type of particle emitted from decay?
  1. Particle decays (Replies: 2)

  2. Decay of particle (Replies: 4)

Loading...