A : Fast moving neutrons do not cause fission of a uranium nucleus.
R: A fast moving neutron spends very little time inside the nucleus.

The decay of proton to neutron is possible only inside the nucleus. Why ?

Mean free path (lambda) in a fission reaction is the average distance covered by a neutron between two fissions. Generation of nearly 200 neutrons are needed to fission all the nuclei in 10 kg of ._(92)U^(235) . If lambda= 4cm and the fastest moving neutrons generated in a fission reaction have an energy of 2 MeV , then the time for 200 neutron generation is found to be pxx10^(-7) seconds. Find 'p' .