Fission is nuclear reactors and atom bombs. Take a heavy element that has a radioactive variant and smush a lot of it together, As each atom gives off radioactive particles, they either zip off into space or they hit another radioactive atom and trigger it to send out a radioactive particle. Smush enough of it together and it will be certain that most particles will hit other atoms. That will cause a chain reaction. Control that by carefully maintaining the distance between the bits, and you have a nuclear reactor. Smush them all together, and you have a bomb.
There are two problems to overcome when making a bomb. One – the reaction blows apart the material, which stops the reaction. Two – how to get the bits smushed together at the right time, over the target and not before?
The solution is to put the radioactive material in a heavy casing to prevent it blowing apart before the reaction can really take hold. We are talking millionths of a second here. And to get the material together in the right place over the target, put most of the material in a case at one end of a tube with a cavity in it.
Put the remaining material at the other end of the tube. When you get to the target, set off a conventional explosion that drives the remaining material at high speed into the cavity in the rest of the material.
That’s fission. It is predictable, and all it needs are the right materials – like Uranium and Plutonium – elements at the dense end of the Periodic Table, with atoms packed closely together just itching to give off their particles.
Fusion uses elements at the light end of the Periodic Table, materials that are very abundant but more difficult to trigger. Hydrogen is the lightest element, and it has two radioactive variants. You get them by sifting seawater.
Smush all the radioactive hydrogen together and nothing will happen. You have to encourage it with energy, exciting the material with temperatures more than three million degrees Celsius. That’s the level of energy needed to get the radioactive hydrogen to fuse to start a chain reaction, make a helium nuclei and give off energy. The trick is to get the reaction to give off more energy that is pumped into it. and that is what has been in the news, with scientists at the Livermore Laboratory getting a tiny bit of radioactive hydrogen to give off more energy that was pumped into it.
If it works at scale it is worth it because one kilo of radioactive hydrogen is equal to ten million kilos of fossil fuel.
A cheap source of energy might encourage mankind to can carry on as before – look Ma, no pollutants. But we are using up the materials – land use – raw materials for making things – etc – that make that future possible, and we are running out of road. And cheap, clean, energy sources don’t solve that problem.