What are fission and fusion? 

When neutrons impact, they form quantum-size kilonova. 

Why are heavy atoms so short-living? The reason for that is that they are large atoms. When radiation or wave movement impacts large atoms it fills them with free energy. Free energy is that thing that causes a thing called fission. 

Of course, everybody knows that fission is splitting heavy atoms. And fusion is to connect nuclei of light atoms. But what happens in those reactions? When free neutron impacts to atom's nucleus, it impacts another neutron. The result is like quantum-size kilonova. That impact fills the nucleus with free energy. And then that thing splits the atom into two or more parts. 

Free energy is the thing that causes natural fission. But when outcoming neutron impacts with another neutron that thing sends massive energy impact through the atom. The quantum fields that connect protons and neutrons to an atom's nucleus are stretching. During that process, those energy fields harvest more energy. During that process, neutrons turn their north poles against each other. And that thing pushes those remnants of nuclei away. 

When two neutrons are impacting, they act like neutron stars. 

When energy impulse travels through atoms the impact time with material depends on two things. 

1) The size of an atom.

2) And the energy level of the atom. 

If an atom's energy level is low. That makes its quantum field expand. That means there is more space for free energy than otherwise. Also, symmetry in those quantum fields is turning full balls. And that thing makes those low-energy atoms harder to fissile than high-energy atoms. 

When energy or shockwave travels through large atoms it interacts with them for a long time, if we compare that situation with the case, when a shockwave travels through small-size atoms. The effect of the shockwave that begins in neutron impact depends on the power of impact, and time of interaction of those shockwaves and particles or their quantum fields. 

Then that thing makes a small electromagnetic vacuum between those atoms' parts. And then energy falls in that channel forming the energy impulse. The thing that destroys atoms is the free energy that suddenly ends. The quantum-size kilonova creates a shockwave around the atom that pulls particles away. And then that shockwave collapses. The reason why neutrons can impact each other with so powerful energy is that they have two poles. 

The south pole turns against the atom because all nuclei have a positive electric load. That means the neutron's speed is enormous. If the neutron doesn't impact with another neutron it can travel through the entire atom. But if two neutrons impact that thing pulls their electricity to one point. And then that electric arc sends a symmetric shockwave through the atom. Impacting neutrons are the thing that forms nuclear fission. 

But in nuclear fusion, the impact with two nuclei releases more energy. The system works like this. When those nuclei impact, their quantum fields expand. That thing rips the superstrings from the protons and neutrons out of the nucleus. The energy released in a fusion reaction is similar thing as soundwave when two cars collide. When we are thinking of the form of fusion, that thing means that the protons and neutrons slip, or tunnel themselves between each other. That thing causes a reaction where a couple of those things turn to wave movement. So that is the thing that sends the energy impulse of fusion.