For a point source at the origin, the three-dimensional neutron diffusion equation be- comes -Dv?e(r) + K Dy(r) = Q8(r). Apply a three-dimensional Fourier transform. Solve the transformed equation. Trans- form the solution back into r-space. The following equations are useful. 1. (2n)2 Svf(r)eikrdr= S-Ik|?f(r)ekr dr. (2n)2 2. Let 0(k) : Se(r)ekr d3r. (2n)7 -ar 3. The Fourier transform of f(r) 1 is (27)2 k2+a2