We will answer these questions soon, but first we need to look into the nature of the
nucleus and quantum mechanics.
Protons are positive and electrically repel one another. A nucleus would blow
apart if it weren't "glued" together by the gluon particles which affect every part
of the nucleus. This is called the residual strong force.
Think of a nucleus as a tightly coiled spring
which is the electrical repulsion, held in place by a very big rope
which is the residual strong force.
Even though there is a lot of stored-up energy in the spring,
it can't release the energy because the rope is too strong.