Calculate the thickness of a cadmium thin film needed to reduce the flux of thermal neutrons by $100$ times. Neutron capture cross$-$section for Cadmium is sigma $=2\mathrm{.}45$ kb $,$ density rho $=8\mathrm{.}65$ g$/$cm$^3,$ and atomic mass $112\mathrm{.}4$ g$/$mol$.$