When certain topics like nuclear physics or chemistry are brought up, I think a lot of people just assume that it’s too hard for them to understand. But that’s not true at all! I strongly believe that if it’s taught the right way, anybody can understand science. I really hope that the resources here are the right ones to get you started.
Nuclear physics reactions are reactions that happen to something called a nucleus, which is a little clump of particles at the center of something called an atom. A reaction is whatever happens when something -- like, for example, a pile of baking soda -- is changed in some way by something else. Like, a whole bunch of vinegar! When you pour that vinegar over the baking soda, it reacts by foaming up into this fizzy, bubbly mess. A nucleus is like the baking soda, and it can be changed in all kinds of different ways.
Particles are like little building blocks. The smallest kind of particle is called an elementary, or fundamental particle, and when you group certain ones together, you can make bigger particles like protons and neutrons. They're both different combinations of a group of fundamental particles called 'quarks', but are still both very different from each other.
Protons and neutrons, together with another type of elementary particle called an electron, make up an atom. While the nucleus is at the center, electrons swirl around the outside like bees buzzing around a beehive; and altogether, they’re so tiny, that it would take billions and billions just to make a single grain of sand!
Certain atomic nuclei are not very stable, which means that they can’t hold all of their protons and neutrons together. When a nucleus isn't strong enough to hold everything in, it has to radiate, or throw some of its particles or extra energy away.
There are lots of different types of reactions that can happen, depending on what an atom needs so that it can be stable again. For example, if a nucleus is too heavy, it will radiate something called an alpha particle, which is made out of a couple of protons and neutrons, so it can be smaller and lighter. If it has too many or too few neutrons, it can turn one into the other by radiating a beta particle, which is either an electron or ‘positron’, and another type of particle called a ‘neutrino’. If an atom just has way too much energy, it fires out very powerful beams of invisible light called gamma rays, which are made out of tiny little particles called ‘photons’. All of these are examples of radioactivity.
When an unstable nucleus loses particles, it’s called a fission reaction. These atoms start with more energy than they’re able to handle, so they gradually fall apart until they’re stable again. Radioactivity from unstable atoms is a form of nuclear fission, but sometimes, stable atoms are made to undergo other types of fission reactions by having single neutrons thrown at them really hard until they break apart into two or more smaller nuclei. This is part of how nuclear power plants generate energy.
Fusion reactions are another type of nuclear reaction, and are basically the opposite of fission. Instead of losing particles, fused nuclei gain some. If you hit two atoms together hard enough, you can make them clump together into a single one. The sun is one very big, long nuclear fusion reaction, and really shows how powerful they are!
Nuclear physics reactions are often also related to chemistry. These types of reactions can sometimes change what chemical element an atom is. Each element has unique characteristics that makes each one of them unique, and what element an atom is depends on how many protons are in its nucleus. So, if an atom gains or loses any protons, it will be a different element than what it was before, with totally new properties. Sometimes, this can be dangerous because radioactive elements can transform into toxic things like lead, or the reaction might be so powerful that it can harm your body with high amounts of energy. They aren’t always bad, though; nuclear power plants use fission reactions to help generate electricity, and radioactive medicine, called ‘radiopharmaceuticals’, can be used to diagnose and treat horrible diseases like cancer!
I know all of this must sound very complicated because of all the terms and particles that you have to memorize. But, just remember that all that really happens is that either something breaks apart and becomes two or more things (fission), or, two or more things clump together and become one thing (fusion). It really is that simple, I promise!