Unit 1 Section 1 Stable and Unstable Nuclei

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The Strong Nuclear Force

  • The strong nuclear force is repulsive for very small seperations of nucleons (less than 0.5fm).
  • As nucleon seperation increases past 0.5fm, the strong nuclear force becomes attractive. It reaches a maximum attractive value and then falls rapidly to zero after 3.0fm.
  • The electromagnetic force in the nucleus extends over a much larger range (infinitely).


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Alpha Decay

  • This only happens in atoms with 82 or more protons, like uranium and radium.
  • The nuclei are too big for the S.N.F. so they emit an alpha particle (helium nucleus) to become more stable.
  • When emitted the proton number decreases by 2 and the nucleon number decreases by 4.


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Beta-minus Decay

  • Is the emission of an electron and an anti-neutrino.
  • This happens in isotopes that are neutron rich.
  • When a beta particle is emitted, one of it neutrons is changed into a proton.
  • The proton number increases by one, and the nucleon number stays the same.
  • The anti-neutrino emitted carries away some energy and momentum.

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