Where Does the l22 Term in the Fluence Rate Numerator Come From?

[Graham87]

Homework Statement

See pictures

Relevant Equations

See pictures

I managed to calculate the fluence of the scattered photons. However, not the transferred photons. In the solution sheet the fluence rate has an l₂² in the numerator in the end of the solution sheet. Where does that come from?

 

[TSny]

I managed to calculate the fluence of the scattered photons. However, not the transferred photons. In the solution sheet the fluence rate has an l₂² in the numerator in the end of the solution sheet. Where does that come from?

Note that $\dot \varphi_0$ is defined to be the fluence rate at the position of the graphite cylinder, which is at a distance $l_1 = l_2$ from the source. Thus, what would be the fluence rate at a distance of $l_3$ from the source, expressed in terms of $\dot \varphi_0$, $l_2$, and $l_3$, assuming no lead shield?