Assume that \(5 \mathrm{MeV}\) gamma (in the form of a narrow beam) is incident on a composite medium of \(2 \mathrm{~cm}\) sodium, \(0.5 \mathrm{~cm}\) of lead, and some unknown thickness of Iron medium. If the uncollided gamma intensity on the other side of the composite shield is \(1 / 150\) th of the incident intensity, then find the thickness of Fe medium used.