A new method of pulsed neutron experimentation is proposed and successfully applied to a beryllium metal system. The present technique utilizes the γ-ray flash from an electron linear accelerator. The employment of an “internal” neutron source, i.e., the (γ, n) reaction in beryllium, which is “softer” than the often used “external” 14-MeV neutrons from a generator, improves the state of the art of the die-away technique in beryllium. The reduction of background neutrons makes it possible to measure the decay curve until ∼ 1800 µsec after a burst even for a small beryllium assembly of 15 × 15 × 15 cm in dimension (B2 = 0.101 cm-2), while in earlier experiments the decay curves have been measured only until ∼600 µsec for such a small beryllium assembly. The present analysis of decay curves indicates that the assumption made by Kothari, who derived the limit of a discrete decay constant for crystalline moderators, is not valid at least for beryllium. On the other hand, Corngold’s limit is consistent with the experimental results.