= Solution
\b[At the stated threshold the idealized system admits a self-sustaining <neutron> mode.] Production and losses balance without the external source. A nonzero continuing source then makes the assumed linear, time-independent response singular rather than selecting a finite equilibrium amplitude.
An apparent infinite steady flux is therefore a failure of that steady linear approximation at the threshold, not a physical prediction that an actual <neutron> population instantly becomes infinite. Time dependence and feedback must be considered to discuss subsequent behaviour.
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