# Steady state diffusion through three layers system

Consider a system that consists of a flat layer of material of thicness L that creates radioactive particles surrounded on each side by a very thic layer of material that absorbs the partices that are produced by the radioactive layer.... see attached

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#### Solution Preview

A condensed version of the solution is provided below. Please see attached for full workings, with equations.

(a) The equations are:

(1.1)

Since the system is invariant under translation in the xy plane, the concentration profile is a function of time (t) and altitude (z) only.

In a steady state, the concentration profile, by definition, does not change with time:

(1.2)

The steady state concentration profile is a function of z alone So the equations for the steady state become standard ordinary differential equations:

(1.3)

For equation (1.3.1) we get:

(1.4)

Since are constants, integrating twice with respect to z yields the general solution:

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#### Solution Summary

The solution shows how to formulate the steady state equation, solve them and apply physical and mathematical conditions to obtain the concentration profile.