Which species is most likely to lose a positron (${\mathrm{\beta }}^{3+}$)?

Positron decay often takes place in big radionuclides that are "proton-rich" because positron emission reduces the proton number compared to the neutron number. Nuclear transmutation, which is caused by positron decay, transforms an atom of one chemical element into an atom of an element with an atomic number that is one unit lower.