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Radiation velocity

  1. Mar 8, 2007 #1


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    What velocity does the electron that is emitted from a beta-decay have? And what velocity does the Alpha particle have when it's emitted?
  2. jcsd
  3. Mar 8, 2007 #2
    beta decay:The spectrum is continuous I think, It depends on the distribution of P, over the neutrino , electron , and the Nucleus.
    But the energy is usually from several 100 Kev to Mev's
  4. Mar 8, 2007 #3

    Meir Achuz

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    The beta decay spectrum is continuous. The electron has a maximum velocity determined by energy conservation. For neutron decay, the maximum electron energy is approximately given by E=M_n-M_p. Then v=p/E with p=\sqrt{E^2-m_e^2}~1-m_2^2/2E, which is close to but a bit
    smaller than 1. (all in units with c=1)
    For nuclear beta decay, put in the masses of the nuclei.

    The alpha particle has a definite velocity. Its energy is the difference in masses of the initial and final nuclei. Then v is found as above, but a nonrelativistic approximation is usually good.
  5. Mar 10, 2007 #4


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    Hmm, I don't know how to use that equation since I know very little of particle physics. How would you approximate a normal velocity for an electron to be when it's released for example from an uranium-238?
  6. Mar 10, 2007 #5


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    See - http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radser.html

    U-238 emits an alpha particle with an energy of about 4 MeV, which is non-relativistic, so one can use the classical kinetic energy E = 1/2 mv2 to calculate a velocity. One could ignore the momentum lost (<2%) to the Th-234 daughter product.

    On the other hand, a 1 MeV beta particle requires a relativistic correction to determine its speed.

    For beta energies, look here - http://hps.org/publicinformation/radardecaydata.cfm

    Select an element, then select the isotopic mass, then 'get data'.
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