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The weak force, first step of nuclear fusion in the Sun

  1. Feb 23, 2014 #1
    Hi. I need help please with a textbook illustration that has confused me.

    Is the caption a typo? Should be "neutrons into protons" instead?


    Attached Files:

  2. jcsd
  3. Feb 23, 2014 #2


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    Staff: Mentor

    The illustration is correct. A helium-2 nucleus, aka a diproton, is not stable, so when two protons collide in the core of the Sun, one of them MUST be turned into a neutron in order for proton-proton fusion to work. Most collisions between protons do not result in fusion. It is only on the very rare occasions that the weak force is able to turn one of the protons into a neutron that fusion occurs.

    See here: http://en.wikipedia.org/wiki/Proton-proton_chain_reaction
  4. Mar 30, 2014 #3

    Thank you for your help. I understand now that it's protons to neutrons.

    My confusion stemmed from the placement of the quarks. Is the proton on the left incorrectly labeled with two down quarks and one up quark--should have two up and one down? Vice versa for the neutron on the right?

  5. Mar 30, 2014 #4


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    Science Advisor

    Yep, you're right. The picture has it backwards!
  6. Mar 30, 2014 #5


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    Staff: Mentor

    Oh wow, I didn't even notice, lol.
  7. Mar 30, 2014 #6
    Oh good, I felt stumped. Nice relief.

    Thank you, both!
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