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Expert: - 3/6/2009


Question
Two protons combine then one turns into a neutron by the release of a positron, electron-neutrino and 0.42MeV of energy. My question is: The neutron has more mass than a proton. The proton-neutron pair have already lost the mass of the ejected positron and neutrino.  Where does the greater mass of the neutron over that of the proton come from?


Answer
Hello,

The difference you are referring to is what is called "the binding energy" of the particular nucleon - in this case the neutron since: delta m =  [m(n) -  m(p)].  What you referenced in terms of "The neutron has more mass than a proton" is what we call the 'mass defect'. The binding energy is the equivalent of that defect or differential (delta m) via:

delta (E) = delta m(c)^2  = [m(n) -  m(p)] c^2

Thus the greater mass over the proton comes from this energy!

viz.


delta (m) = delta E/ c^2  

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Philip A. Stahl

Expertise

I specialize in stellar and solar astrophysics. Can answer any questions pertaining to these areas, the spectroscopic analysis of stars – as well as the magneto-hydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions.

Experience

Have published papers on the relationship between sunspot morphology and solar flares; discovery of SID flares related to this, constructed computerized stellar models; MHD research.

Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Publications
Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level'.

Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society

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