According to Fick's law of diffusion, how is the neutron flux represented?

Fick's law of diffusion describes how particles such as neutrons diffuse through a medium. The equation that correctly represents neutron flux in this context is derived from Fick's first law, which states that the flux of a quantity is proportional to the negative gradient of that quantity. In this case, the neutron current density (flux) is represented mathematically as the product of the diffusion coefficient and the negative gradient of the neutron density (or potential).

Thus, when we express neutron flux (j) as j = -D ∇φ, we are indicating that the flow of neutrons is moving from regions of higher concentration (or flux potential, φ) to regions of lower concentration, facilitated by the diffusion coefficient (D). This negative sign emphasizes the opposite direction of flux flow concerning the gradient, highlighting that diffusion occurs down the gradient.

Understanding this law is crucial in nuclear engineering as it helps in modeling how neutrons move within a reactor, impacting critical processes such as moderation and absorption. This relationship is foundational when assessing neutron behavior under varying conditions within the reactor core.