# Simple english c01/Nucleus
## Nucleus

The nucleus is in the middle of an atom. It is made up of protons and neutrons. Usually in nature, two things with the same charge repel or shoot away from each other. So for a long time it was a mystery to scientists how the positively charged protons in the nucleus stayed together. They solved this by finding a particle called a Gluon. Its name comes from the word glue as Gluons act like atomic glue, sticking the protons together using the strong nuclear force. It is this force which also holds the quarks together that make up the protons and neutrons.
The number of neutrons in relation to protons defines whether the nucleus is stable or goes through radioactive decay. When there are too many neutrons or protons, the atom tries to make the numbers the same by getting rid of the extra particles. It does this by emitting radiation in the form of alpha, beta or gamma decay.
Nuclei can change through other means too. Nuclear fission is when the Nucleus splits into two smaller nuclei, releasing a lot of stored energy. This release energy is what makes nuclear fission useful for making bombs and electricity, in the form of nuclear power. The other way nuclei can change is through nuclear fusion, when two nuclei join together, or fuse, to make a heavier nucleus. This process requires extreme amounts of energy in order to overcome the electrostatic repulsion between the protons, as they have the same charge. Such high energies are most common in stars like our Sun, which fuses hydrogen for fuel.

## Radioactive decay

Some elements, and many isotopes, have what is called an unstable nucleus. This means the nucleus is either too big to hold itself together or has too many protons, electrons or neutrons. When this happens the nucleus has to get rid of the excess mass or particles. It does this through radiation. An atom that does this can be called radioactive. Unstable atoms continue to be radioactive until they lose enough mass/particles that they become stable. All atoms above atomic number 82 (82 protons) are radioactive.
There are three main types of radioactive decay; alpha, beta and gamma.
* Alpha decay is when the atom shoots out a particle having two protons and two neutrons. This is essentially a Helium nucleus. The result is an element with atomic number two less than before. So for example if a Beryllium atom (atomic number 4) went through alpha decay it would become Helium (atomic number 2). Alpha decay happens when an atom is too big and needs to get rid of some mass.
* Beta decay is when a neutron turns into a proton or a proton turns into a neutron. In the first case the atom shoots out an electron, in the second case it is a positron (like an electron but with a positive charge). The end result is an element with one higher or one lower atomic number than before. Beta decay happens when an atom has either too many protons, or too many neutrons.
* Gamma decay is when an atom shoots out a gamma ray, or wave. It happens when there is a change in the energy of the nucleus. This is usually after a nucleus has already gone through alpha or beta decay. There is no change in the mass, or atomic number or the atom, only in the stored energy inside the nucleus.
Every radioactive element or isotope has something called a half life. This is how long it takes half of any sample of atoms of that type to decay until they become a different stable isotope or element. Large atoms, or isotopes with a big difference between the number of protons and neutrons will therefore have a long half life.
* Structure and parts