Question

Some neutrons were captured by protons to form deuterium nuclei. a. Find the mean time for neutron capture if the cross-section is 10^-28 cm62, the temperature is 10^9 K, and the baryon mass density is 2*10^-5 g/cm^3. Assume the proton to neutron ratio is 5:1, and that the mean time is given by the time for the neutron to travel one mean-free-path.