Using the authors’ recently suggested thermal neutron scattering kernel for liquid hydrogen, which explicitly takes into account the presence of collective motions and two elastic field quantum exchange processes, an extensive study is made on the thermal neutron transport processes by solving the appropriate multigroup Boltzmann transport equation in liquid para and liquid para-orthohydrogen mixtures. The calculated values of the asymptotic decay constant of a neutron pulse in liquid parahydrogen and a 47% para and 53% ortho mixture at 20 K for different assembly sizes are found to agree with the corresponding measured values of Bryan and Waltner, when the chemical binding energy represented by the Debye temperature, θD, is equal to 80 K. The critical buckling for liquid parahydrogen (= 0.16 cm-2) is much smaller in comparison with that of the mixture (=0.8 cm-2). The thermalization time, τth in µs, as calculated by using the eigenvalue spectrum and corresponding eigenfunctions in both liquid parahydrogen and the mixture, increases linearly with buckling but with different slopes and can be represented, respectively, as s/b τth = (68.0 + 750 B2) and τth = (68.0 + 180 B2). Unlike the case of ice at 20 K, there is only one discrete mode in both liquid parahydrogen and the mixture.The calculated values of the diffusion length for natural absorption in pure parahydrogen and in a 47% parahydrogen and 53% orthohydrogen mixture are 5.8 and 2.4 cm, respectively. From the space-dependent spectra studies, it is found that the asymptotic spectra in both the systems for natural absorption are reached in a distance about twice the value of the respective diffusion lengths. The value of critical absorption in parahydrogen is only 1.5 times the natural absorption, while in the mixture it is very large and is greater than ten times the natural absorption. The steady-state calculations were made in liquid parahydrogen at 20 and 11 K, and liquid para-ortho mixtures at 20 K. The computed steady-state spectra at these temperatures for assembly size B2 = 0.133 cm-2 turn out to be in good agreement with the corresponding experimental spectra of Whittemore. As the temperature of liquid parahydrogen is decreased from 20 to 11 K, the effective temperature of the spectra decreased from 34 to ∼25 K, resulting in a substantial increase of cold neutrons. In addition, several studies on steady-state spectra for different sizes of liquid para- and orthohydrogen assemblies, H2-D2 mixtures at 20 and 11 K, and solid H2, D2 at 4 K were made to assess the production of intense beams of cold neutrons. As D2 is added to liquid parahydrogen, the effective temperature of the spectrum decreases for buckling values <0.005 cm-2 at 20 K, 0.002 cm-2 at 11 K, and 0.001 cm-2 at 4 K. For infinite size, pure D2 is the most intense cold neutron source, as the effective temperature will closely correspond to the temperature of the assembly at 20 and at 11 K, and at 4 K it will correspond to ∼6 K. For a practicable size of B2 = 0.0158 cm-2, however, it is found that parahydrogen, or any ortho-para mixture at 11 K is the best source of cold neutrons, better than even the optimum mixture of H2O-D2O. The increase is by more than an order, at very low energies, making it the practicable source for most intense beams of cold neutrons.