Weak interaction

Weak interaction, the weak force or weak nuclear force, is one of the four fundamental forces in the universe. 
It is carried by particles known as the W and Z bosons, which are gauge bosons. The weak force causes beta decay, a form of radioactivity. At extremely high energy levels, the force of weak interaction and electromagnetism begin to act the same, and this is called electroweak interaction.
Beta decay.
Beta decay is what scientists call a neutron breaking down, in contrast with alpha decay where an atom breaks down. These types of breaking down are more commonly known as radioactive decay. In a beta decay a neutron breaks into a proton, an electron and a neutrino. However, this is not a complete picture, there is an intermediary step. Notice that this process preserves the total charge. Conservation laws are very important when calculating the possible outcomes of these interactions.
With more detail, beta decay begins with a neutron, which is made of one up quark and two down quarks. Since up quarks have a charge of +2/3, and each down quark has a charge of -1/3 this results as giving 2/3 -1/3 -1/3 = 0 charge. Due to weak force, if there are too many neutrons in an atom nucleus, one of the down quarks in one of the neutrons turns into an up quark. This would change the charge of the neutron from 0 to (2/3 +2/3 -1/3) = 1. From this, the neutron is no longer a neutron, but actually a proton ( a particle with a charge of +1). 
In a strange quantum effect, this transformation releases a particle called a W boson. This is the gauge boson (force-carrying particle) of weak force. Oddly, the W boson has a mass about 80 times as much as a neutron. This sort of thing actually happens very often in quantum mechanics, but it follows the conservation of energy because it happens so quickly. After 3x10–25 seconds, the W boson breaks into an electron and an electron antineutrino. (The electron antineutrino doesn't really do much). This releases the electron and basically creates a proton from a neutron.