H3) contains 1 proton and 2 neutrons. In a neutron decays as n → p + e + v , the nucleus may have 2 protons and one neutron, i.e., tritium will transform into
‌
2
He3 (2 protons and 1 neutron). Triton energy is less than that of
‌
2
He3 nucleus, i.e., transformation is not allowed energetically.