The diffusion coefficient in a vacuum

[Faisal Moshiur]

Homework Statement

Write an equation expressing the neutron current in an infinite vacuum for a point source. (Hint: There is no diffusion coefficient term as the medium is an infinite vacuum.)

Relevant Equations

Φ = S / (4 π r^2 )
J = -∇Φ

J = Φ.n, where n is a unit vector normal to the flow of flux.