Prof. Kippot decides to carry out his task measuring the neutron current at the external surface of the rock. He considers this large rock to be semi-infinite (i.e. the domain is x[0,), where x=0 corresponds to the rock external surface). It is also known that for this system the ratio between the diffusion coefficient and the macroscopic absorption cross section is Da=100 cm2. In order to solve the equation found in Q5a, the two the boundary conditions were considred as follows:

* for x the solution must be finite.

* at x=0: =0.

Prof. Kippot solves the system and finds the solution to be:

(x)=Sa(1e(xaD))

At the external surface (x=0), Prof. Kippot measures a neutron current (J(x) ) equal to 5 cm2s1 (that is: 5 cm2s1 in the x direction ).

What is the estimated intensity of the source (S) ? Specify the answer in units of cm3s