12.4 Two large gray parallel plates at temperatures T and T and with emissivities & and & are separated by an optically thick gray medium with absorption and isotropic scattering. The medium has within it a uniform volumetric energy source of 9 W/m. Compute the tempera- ture distribution in the medium by use of the diffusion method with jump boundary condi- tions for the limit of negligible heat conduction.