41 - Radiation

For flat surfaces \[\begin{aligned} F_{11} = 0 &\text{ } F_{12} = 1 \\ F_{21} = 1 &\text{ } F_{22} = 0 \end{aligned}\]

For cylinders & spheres \[\begin{aligned} F_{11} = 0 &\text{ } F_{12} = 1 \\ F_{21} = A_1/A_2 &\text{ } F_{22} = 1 - A_1/A_2 \end{aligned}\]