In particular, the weak force can change one quark type into another. Protons and neutrons are made of two quark varieties, up and down. The weak force can turn a down quark in a neutron into an up quark, which would change the neutron into a proton and switch its electric charge from neutral to positive. If that neutron were in the nucleus of an atom, the change to a proton would turn that atom into a different type of element. Such reactions are happening all the time in our Sun, giving it the energy to shine. This type of action also occurs in radioactive decay, which happens when atoms spontaneously shed energy and subatomic particles.