> Decay rates become very slow when the children from a decay have masses that add up very close to that of the parent; that’s not surprising, since by rule 2 the decay rate has to decrease to zero once the children have more mass than the parent.
But the really odd thing is that if you put a neutron in certain atomic nuclei, it becomes stable! Helium, for instance, has two protons and two neutrons. Even though a neutron by itself lives a quarter of an hour, a helium nucleus will live for the age of the universe and longer. In fact this is true for the neutrons in the nuclei of all of t…