During a series of experiments with tritium (t) in deuterium (d) plasmas in the Joint European Torus (JET), the temporal evolution and the two-dimensional (2-D) spatial profiles of the 2.5 and 14MeV neutron emissivity from d-d and d-t fusion reactions were inferred from measurements with the JET neutron emission profile monitor. These experiments, involving triton production from d-d fusion, beam deposition and diffusion, d-t fusion, and tritium removed from wall tiles, were investigated in four plasma scenarios: (i) In high performance deuterium plasmas with deuterium neutral beam injection, the 14MeV neutron emissivity due to triton burnup was observed. (ii) In discharges with 1% tritium beam injection, neutron emissivity ratios showed that approximately the same deposition profiles resulted from tritium as from deuterium beams. A thermalized-tritium diffusion experiment was performed in which the tritium-deuterium density ratio was found to be spatially constant across the plasma; in conjunction with similar particle source profiles, this indicates that deuterium and tritium have similar particle transport properties. (iii) In two high performance discharges for which two of the sixteen neutral beam sources operated with 100% tritium, the production rate of 14MeV neutrons reached 6·1017n·s­1. The a-particle 2-D birth profile was directly inferred from the measured 14MeV neutron emissivity profile. Both the axial 14MeV neutron emissivity and the axial ion temperature saturated before the maximum global emission was reached. (iv) During the tritium cleanup phase, residual tritium entering the plasma produced a spatially constant ratio of tritium to deuterium, confirming the similarity of their particle transport properties.