Sometimes when diagnosing certain types of diseases, stable atoms in your body are replaced by radioactive atoms of the same element.
These radioactive elements then move around throughout your body as they would normally, but because they are radioactive, they're easier to detect outside of the body.
Also, those neutrons that were ejected can be used to initiate several other fission reactions.
This 'domino effect' caused by the neutrons is called a chain reaction, and it can be responsible for keeping the reaction going for a long time.
Now, carbon-14 has a half-life of about 5,730 years, so every 5,730 years, half of it is going to decay into nitrogen.
The more carbon-14 that an artifact has, the more recent it is.
The sun is essentially a fusion reactor creating energy by fusing hydrogen atoms together to form helium, and the sun is our primary source of energy.
We use the sun's energy for solar power, photosynthesis, and even in the fossil fuels we burn.
Fossil fuels are really just dead organisms that once used the sun for energy and that have been under a great deal of pressure by being buried under rocks.
So, right now on Earth, we can't run our own nuclear fusion reactors, but we still rely heavily on the fusion reactions that take place on the sun.
Whenever nuclear power is discussed, whether it be in the form of a nuclear reactor or a nuclear-powered submarine, the energy is produced because of a fission reaction.