Emissivity of a cylindrical black-body cavity with a re-entrant cone and face

The emissivity epsilon of a cylindrical black-body cavity with a re-entrant cone and face is calculated assuming that the surface is both isothermal and diffusely reflecting. The results are presented in the form epsilon =(1-I1 rho -I2 rho 2) where rho is the surface hemispherical reflectivity. Values for I1 and I2 are tabulated as a function of the length of the cavity, the height of the cone and the position of sighting on the cone surface. I1 and I2 have also been calculated for the case when the open end of the cavity is reduced by an aperture plate.