# Homework Help: Derivation of neutron flux equation

1. Nov 4, 2016

1. The problem statement, all variables and given/known data
reactor consists of nested spheres (sorry, this is my first time posting):

Sphere 2 --> Actinide Fuel surrounding lead target; has outer radius of R1 (A-region)
Sphere 3 --> Reflector surrounding the fuel with outer radius of R2 (E-region)
Neutron flux vanishes at radius R2

Derive the neutron flux equation in A-region

2. Relevant equations
the neutron flux at A-region is given as:

Φ(r) = S/4πD [1/r - 1/R2]

3. The attempt at a solution
I've attempted this solution assuming the lead target as a point source so I get Φ(r) = B e-r/L
where I determine the constant 'B' using neutron current going to zero at radius R2, but I always end up with a final answer containing exponentials.........I'm really stuck even though this was supposed to be a very simple derivation we were to get to work on in the class hour (prof made it a take home aspect)

2. Nov 10, 2016