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Question on KE of radioactive source

  1. Jan 3, 2005 #1
    an alpha particle from a certain radioactive source has a Kinetic energy of 8.2x10(-13)j. Using the information below, estimate how long it would ctake this particle to travel a distance equal to the diameter of the atom.
    mass of alpha particle= 6.6x10-27kg
    diameter of atom=1x10-10m
    my answer
    (9.2X10-13X2)/6.6X10-27= THE Square root of 2.48
    which is obviously wrong, can u guyz help me adress the problem?
  2. jcsd
  3. Jan 3, 2005 #2


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    Staff: Mentor

    Determine the velocity, [tex]v = \sqrt{\frac{2\,KE}{m}}[/tex]

    and then t = v / d.

    You may have a numercial error in (9.2X10-13X2)/6.6X10-27

    KE = 8.2x10-13 J = ~ 5.1 MeV, so it is non-relativistic.

    m = 6.6x10-27 kg
  4. Jan 4, 2005 #3
    I dont get it?
  5. Jan 5, 2005 #4


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    Staff Emeritus
    Science Advisor

    Several points: first,you have "9.2" when I think you mean "8.2". I think that's just a typo since the "2.48" is correct.

    Second, however, (9.2X10-13x2)/6.6X10-27 is not any where near "2.48"! Did you forget or simply not write the 10-13/(6.6X10-27? I get 2.48X1014.
    The square root of that is 15763402 m/s.

    Finally, according to your formula, that is the speed of the alpha partical. You were asked to find the time it would take to cross the diameter of an atom.
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