An equilateral triangle of side length 'l' is located at the center and at the midpoint of one side, where neutron sources of strengths S [neutrons/second] are placed at each one of the vertices. Carry out the following calculations:
a. In a vacuum.
b. In a diffusing medium with a diffusion coefficient D and a diffusion length L.
Note: Fick's law applies only in the case of a diffusing medium.