There are several types of beta decay transition. In a Fermi transition, the spins of the two emitted particles are anti-parallel, for a combined spin S = 0 . As a result, the total angular momentum of the nucleus is unchanged by the transition. By contrast, in a Gamow-Teller transition, the spins of the two emitted particles are parallel, with total spin S = 1 , leading to a change in angular momentum between the initial and final states of the nucleus.