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# Physics/Binding energy vs binding energy per nucleon

Question
In my textbook it says that tritium has more binding energy than He-3 , but I don't get it! Isn't binding energy the amount of energy needed to separate the nucleons? Tritium releases energy to form He-3, it doesn't need energy to separate itself it does that naturally, but when looking at the inverse reaction He-3  requires energy to form tritium. My question now is , is the binding energy of tritium more than He-3 because tritium has more mass, and the binding energy PER NUCLEON for He-3 is larger than that for tritium because wee need  energy for it to form tritium , or I got all of this wrong? Please explain because I know that more stable atoms have more binding energy, so how come tritium has more if it is less stable than Helium-3 ?

It does have more binding energy, which is why the 3He(n,p)3H reaction works to detect neutrons in a 3He Geiger counter.  You don't have two protons with their Coulomb repulsion in the same nucleus that way.  It's energetically favorable to replace one of the protons in 3He with an available neutron, hence the difference in binding energy.  However, a neutron has more mass than a proton.  It is still energetically favorable to convert a neutron into a proton during a weak (beta) decay.  The maximum energy of beta decay for tritium is less than the mass-energy difference between a neutron and a proton.  The difference between those two energies (the total energy released in a tritium beta decay between all three outgoing products and the mass-energy difference between the proton and neutron) is equal to the difference in the binding energy between 3H and 3He.

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#### Dr. Stephen O. Nelson

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