Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Positron emission

  1. Sep 26, 2010 #1
    I've been wondering about positron emission. If a neutron has more mass than a proton, how can a proton turn into a neutron by releasing a particle with mass?
    [PLAIN]http://img37.imageshack.us/img37/654/positronemission.gif [Broken]
    (source:http://en.wikipedia.org/wiki/Positron_emission)
    Doesn't this violate the law of conservation of energy? Isn't Boron-11 heavier than Carbon-11?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 26, 2010 #2

    jtbell

    User Avatar

    Staff: Mentor

    Look them up. :smile:

    http://www.nist.gov/physlab/data/comp.cfm [Broken]

    For C you need to use the "All isotopes" option.
     
    Last edited by a moderator: May 4, 2017
  4. Sep 26, 2010 #3
    But... Doesn't Boron have 6 neutrons and 5 protons, where Carbon has 5 neutrons and 6 protons? What am I missing here? Apologies, but my knowledge of nuclear physics is elementary, at best.
     
  5. Sep 26, 2010 #4

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    Cylinder, jtbell gave you some excellent advice. Look them up.
     
  6. Sep 26, 2010 #5
    Yes, I looked them up before I posted that. I'm sorry, I was just stating that I am confused about something else now: it looks like the masses of the nucleons don't add linearly. I understand if my new question is a bit off topic. Should I start a new thread?
     
  7. Sep 26, 2010 #6
    Last edited: Sep 26, 2010
  8. Sep 26, 2010 #7
    The concept of nuclear binding energy is the piece you seem to be missing:

    http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html

    has a pretty good overview for this and the basics of nuclear mass and how it relates to nucleons.

    Essentially, this binding energy (mass) difference is the source of the energy for both fusion and fission.
     
    Last edited: Sep 26, 2010
  9. Sep 26, 2010 #8

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    The total mass of a nucleus is LESS than the total mass of the individual particles that make up the nucleus if they were not bound, because of nuclear binding energy.
     
  10. Sep 26, 2010 #9
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook