Hydrogen to Helium

  1. I am a freshman and in physical science but we have not yet come to fusion or anything like that. One day I jsut started to think.. what if you took an ordinary hydrogen atom (not an isotope.) and added 1 proton, 1 electron, and 2 neutrons in whatever way you could. Would you get helium, or just a very strange hydrogen atom, or what?
     
    Last edited: Sep 26, 2008
  2. jcsd
  3. mgb_phys

    mgb_phys 8,952
    Science Advisor
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    Yes you get helium, it's quite easy to do in large quantities if you have the correct equipement ( a star)
     
  4. Thats kind of cool.. would you happen to know how? and if so would you care to try to explain it to me?
     
  5. Astronuc

    Staff: Mentor

    The isotopes of hydrogen are protium (the atom is comprised of one electron orbiting a single proton), deuterium (one electron orbiting a nucleus composed of one proton and one neutron), and tritium (one electron orbiting a nucleus composed of one proton and two neutrons). In all three isotopes, the single proton provides the positive charge which is equal in magnitude but opposite of the electron.

    The helium nucleus contains two protons. He-3 has a nucleus containing 2p+n, while the very common, He-4 had a nucleus (2p, 2n).

    Adding p + p + 2n into one nucleus will give (2p,2n) = α, which is the nucleus of He-4.


    Stars use the proton-proton cycle with interim steps to produce He-4, and there is a second cycle (CNO) in which protons are fused into the nuclei, the last one of which experiences a (p,α) reaction.

    http://csep10.phys.utk.edu/astr162/lect/energy/ppchain.html
    http://csep10.phys.utk.edu/astr162/lect/energy/cno.html

    http://hyperphysics.phy-astr.gsu.edu/hbase/astro/procyc.html
     
    Last edited: Sep 26, 2008
  6. Protons by themselves aren't going to stick together, the system of two protons and no neutrons is not stable (don't ask me why).

    You can add a neutron to each proton and make two deuterium atoms. Those are stable. You should be able simply to expose a hydrogen tank to neutron radiation to produce deuterium. I'm not sure how big the cross section is. In practice it's much easier to electrolyze ordinary water and separate deuterium from protium. There's always a measurable amount of deuterium in the water.

    If you then take a quantity of deuterium and heat it to a very high temperature, deuterium nuclei will start smashing into each other and occasionally fuse together into helium. They are positively charged and electrostatic force will work to keep them apart. You need high temperature (i.e. high velocities of individual molecules) to bring them together close enough for d+d -> He reaction to go through. You don't start seeing significant conversion rates till you heat plasma to millions of degrees.

    Then you cool the resulting mix (plasma consists of ionized nuclei and free electrons), electrons will naturally form orbits and create atoms.
     
    Last edited: Sep 26, 2008
  7. mgb_phys

    mgb_phys 8,952
    Science Advisor
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    The details depend on the exact temperature and pressure of your particular star. The important point is that all electorns, protons, nuetrons are the same and all heavier atoms are built up from hydrogen by similair processes in stars.

    (ok - except some He3 that was formed in the big bang)
     
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