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Homework Help: Photon Smashing into Particle

  1. Apr 23, 2010 #1
    An energetic photon strikes a helium nucleus and breaks into two hydrogen isotopes (A = 2, Z = 1). The two particles move off at 0.6c. Assume all energy of the photon is absorbed and that relativistic energies are involved.

    Q - what is the wavelength of the incoming photon?

    Conservation of energy - Ei = Ef
    E(photon) + E(helium) = 2E(hydrogen)

    E(photon) = 2E(hydrogen) - E(helium)

    hc/[tex]\lambda[/tex] = 2([tex]\gamma[/tex]m(H)c^2) - ([tex]\gamma[/tex]m(He)c^2)

    [tex]\gamma[/tex] = 1/sqrt(1-u^2/c^2)

    Then I would solve for [tex]\lambda[/tex] by rearranging the equation.
    Is this how i should be solving this type of problem?

  2. jcsd
  3. Apr 23, 2010 #2


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    Hello DoubleMint,

    Was the Helium nucleus (which exists before the collision) initially at rest? You have a [tex] \gamma [/tex] in the helium associated term. And even if it wasn't at rest, it wouldn't have the same [tex] \gamma [/tex] as the one associated with the hydrogen nuclei, would it?
  4. Apr 23, 2010 #3
    Hi collinsmark,

    The helium nucleus is initially at rest, so would it be just be the rest energy of the particle, E = mc^2?
    If it was not at rest, [tex]\gamma[/tex] would not be the same. Sorry about that!
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