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Nuclear Force
Proton – Nucleon and Neutron – Nucleon
Interactions
Nuclear force
But why does this happen? All particles are surrounded by
force fields. A proton exerts both electrostatic force and strong
force (nuclear force), but a neutron exerts only strong force and
does not feel any electrostatic interaction, because it is not
carrying charge.
The nuclear force is a force far stronger than electromagnetic
forces, but it has a very short range of action. In fact, it acts
only on distances of the order of the radius of an atomic
nucleus (about 10-14 m = fm).
Nuclear
force field
Neutron
Electric
field
Proton
Nuclear Potential Energy
So there will be a potential well very near the centre of a nucleon and
when another nucleon approaches that well it will fall in it (if the energetic
conditions are right).
It’s a bit like playing golf:
• if a proton approaches another proton the hole is at the top
of a hill and a golf ball shot with too little velocity will lose KE
and gain PE as it climbs up and fall back down.
Proton – Proton interaction
Nuclear Potential Energy
• if the KE of the ball is sufficient, the ball will reach the top of
the hill and fall in the hole.
• In other words, if the proton has enough KE to enter the
nuclear force field, it will be trapped by the nuclear force and
fall in the nuclear potential well.
Proton – Proton interaction
Nuclear Potential Energy
• if the approaching nucleon is a neutron, things are a lot
easier, because the potential well will be in a “flat surface”. It
doesn’t matter if it is approaching a proton, because it will not
feel its electrostatic field.
• However, if the neutron is too fast (high KE), it will go past
the potential hole. This is normally the case, because
nucleons outside their nuclei have usually very high KE as it
takes a lot of energy to separate them from the nucleus in the
first place.
Neutron – Proton, or Neutron - Neutron interaction
Nuclear Potential Energy
• However, it is possible to slow the neutron down, so that the
nuclear force will grab it and cause it to fall in the potential
well. This method is used in nuclear power stations and
nuclear bombs to start a chain reaction.
Neutron – Proton, or Neutron - Neutron interaction