Fluctuations of the Number of Neutrons in a Pile

Statistical fluctuations in the number of neutrons in a pile which is just under critical and contains distributed neutron sources such as spontaneous fissions, $\alpha -n$ reactions, etc., are considered for the following two cases: (a) The delayed neutrons are taken into account, but the pile is assumed to be operating at a steady power, and (b), the power at which the pile operates is assumed to change periodically, but the delayed neutrons are neglected.