[en] The diffusion and annihilation of a pair of correlated triplet excitons in anthracene and tetracene crystals has been studied by solving the diffusion equation by the prescribed diffusion method. These results were used to calculate the magnetic field effect on the yield of fission of singlet excitons into a triplet pair in anthracene crystals. This description of the triplet pair kinematics was also used to explain the presence of a slow component in the prompt fluorescence decay of tetracene crystals