In a nuclear reactor, the neutrons produced in fission reaction have high kinetic energy of the order of few MeV. Whereas the `U^(235)` nucleus fissions only iwht a slow neutron. In a reactor heavy water `(D_(2)O)` is used to slow down the neutrons. A neutron hiting a deuterium nucleus slows down quickly. Calculate now many head on, elastic collisions must a neutron have with deuterium nuclei to reduce does not lose energy by any other way apart from collisions with deuterium.
[Take `"log"_(10)2=0.301` and `"log"_(10)3=0.477`]

Answer

8