The force acts over a very short range. Within the nucleus, the force acts between a nucleon and its very nearest neighbours. The range of the force is only about 1 x 10 -15 m or about the diameter of a proton.
The electric force is different in that it acts between all charged pairs and over any distance.
(a) Given that the rest mass of a proton is 1.67268 x 10 -27 kg and the rest mass of a neutron is 1.67499 x 10 -27 kg, determine the mass defect for the helium isotope ( 2 He 4 ) whose rest mass is 6.64489 x 10 -27 kg.
(b) What is the binding energy for the helium nucleus in MeV?
By inspection, 26 Fe 56 has a higher binding energy per nucleon than 1 H 2 . This means that there is a greater mass defect for the iron nucleus when compared to the heavy hydrogen nucleus. So, to remove a nucleon from each nucleus, more mass needs to be replaced for iron. This will require more energy, so the iron nucleus is more stable.
If a particle radioactively decays, its initial momentum before it decays is zero. This means the total momentum after the decay is also zero. As momentum is a vector quantity, we must consider both magnitude and direction.