A Gamow–Teller transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin , leading to an angular momentum change  between the initial and final states of the nucleus (assuming an allowed transition).
In this case, the nuclear part of the operator is given by
with  the weak axial-vector coupling constant, and  the spin Pauli matrices, which can produce a spin-flip in the decaying nucleon.