Difference between parallel and antiparallel spins?

  • #1
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Main Question or Discussion Point

What is the difference between parallel and antiparallel spins for a pair of nucleons?

My understanding is that nucleons have a strong tendency to pair - proton with proton, neutron with neutron, proton with neutron. When they pair their spins either:

cancel (spins pair antiparallel) pairing of a spin-up and spin-down nucleon
add (spins pair parallel) pairing of two nucleons with both spin up or both spin down

Am I understanding this correctly? - I'm thinking I might be missing something in regards to the Pauli Exclusion Principle. How can two nucleons with the same spin state pair?
 

Answers and Replies

  • #2
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How can two nucleons with the same spin state pair?
They cannot.
You can have two nucleons in different (spatial) states with the same spin orientation, however.
 
  • #3
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So nucleons have a strong tendency to pair due to the nuclear force, which has a spin component. When nucleons pair their spins will either be:
(Parallel) - Both spin the same way
(antiparallel) - One nucleon spin up and one spin down

Is there an energy difference between the two as well?
 
  • #4
594
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A more important question - Why are nucleons with parallel spin more strongly bound to each other than those having anti-parallel spin.
 

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