The tritium "weak decay"
The example of tritium, the simplest of radioactive nuclei, shows how nature occasionally uses the ‘weak forces’ to change the proportions of protons and neutrons. One may suppose that tritium, given the fact that it contains one proton and two neutrons, could eject one of its two neutrons to reach stability. Such an expulsion, however, would require too much energy to occur, and so one of the neutrons is transformed into a proton, accompanied by the release of a beta electron and an antineutrino. This process releases enough energy to occur and make tritium radioactive; an instability that is caused by the weak force.