The half life of neutron is $693$ seconds. What fraction of neutrons will decay when a beam of neutrons, having kinetic energy of $0.084\,\text{eV}$, travels a distance of $1\,\text{km}$? (mass of neutron $= 1.68 \times 10^{-27}\,\text{kg}$, and $\ln 2 = 0.693$)