The reason there aren't a bunch of pure neutron particles in our everyday experience is due to a phenomenon known as neutron decay. Neutrons, which are neutral subatomic particles found in the nucleus of atoms, can decay into other particles through the weak nuclear force. The most common decay mode for a neutron is into a proton, an electron, and an electron antineutrino.
The decay of neutrons occurs because they are slightly more massive than the combination of a proton, an electron, and an electron antineutrino. This mass difference allows the neutron to transform into these particles, following the laws of conservation of energy and momentum.
In stable atomic nuclei, neutrons are typically surrounded by protons, forming a balance between the attractive strong nuclear force that holds them together and the electromagnetic repulsion between protons. The presence of protons helps stabilize neutrons, preventing them from decaying spontaneously.
However, outside of atomic nuclei, free neutrons do undergo decay. Their average lifetime is around 14 minutes, after which they transform into a proton, an electron, and an electron antineutrino. This decay process limits the existence of free neutrons in our everyday environment.
It is worth noting that in certain extreme environments, such as the dense cores of neutron stars, a large number of pure neutrons can exist. These conditions result in a state known as neutron degeneracy, where the pressure from gravity prevents the decay of neutrons. But in ordinary conditions found on Earth, free neutrons are unstable and undergo decay relatively quickly.