The isospin of the proton (the 1H nucleus) is 1/2; the isospin of the 2H nucleus is 1.

it is isospin - In physics, and specifically, particle physics, isospin (isotopic spin, isobaric spin) is a quantum number

Proton: e +1, spin 1/2, isospin 1/2, parity +1

Neutron: e 0, spin 1/2, isospin 1/2, parity +1

Electron: e -1, spin 1/2, L +1

You would get 18O, a stable nuclide with isospin 1.

Elements of neutrinoless double beta decay in charge-exchange, the isospin-forbidden single Fermi transition matrix element.