We have performed integral measurements of pulsed neutron distributions in graphite stacks ranging in buckling from 0.0051 to 0,018 cm−2 and have compared the results to a modeled theoretical computation. Based on these measurements, we have defined a critical buckling of 0.0085 cm−2 above which the decay of the neutron pulse is non-exponential. Non-exponential decay was observed in six graphite stacks which exceeded the critical buckling, while in three larger assemblies the decay was exponential over a significant part of the total measuring interval. From measurement of the time-dependent spatial distribution in four graphite assemblies, we were able to compute the effective decay constants of the two lowest order spatial modes as well as the time-dependent effective wave number of the distributions. We have interpreted the failure of the neutron distribution to establish either an exponential decay or an asymptotic spatial distribution in terms of recent theoretical work in this area.