The guide propagation properties of neutron waves and x-rays are described. In spite of apparent resemblance to optical dielectric waveguides, these new neutron/x-ray waveguides have several interesting features. First, the modal dispersion function has the same form as those of the media composing the guide. Second, there is no cutoff wavelength. Third, the neutron waves/x-rays with different wavelengths may be guided with the same mode number and effective coherent nuclear scattering length densities. Fourth, the energy distribution on the cross-section of the guide is independent from the neutron waves/x-rays wavelength, which leads to an energy transfer by channels through the thin film neutron/x-ray guide.