Static and dynamic experiments with a repetitively pulsed neutron booster

A series of dynamic measurements has been performed with a multiplying assembly in which a rotating beryllium reflector (worth 4.8 dollars in reactivity) moved past an unreflected core surface ∼60 times/sec at a speed of 264 m/sec. A pulse of 14.1-MeV neutrons was injected into the assembly each time the rotating reflector attained a position for which the reactivity of the assembly was maximum. The time distribution of neutrons after the injection of the pulse was measured in the core and adjacent to a 10.16- × 10.16- × 3.81-cm polyethylene scatterer which provided a pulse of thermal leakage neutrons. The maximum prompt-neutron multiplication of the assembly, which was reflected with iron on all sides but one and contained 58.6 kg of highly enriched uranium metal at delayed criticality, was varied from 75 to 285 by fuel loading changes. This assembly with a maximum prompt-neutron multiplication of 285 produced fast-neutron pulses with a width at half-maximum of 3.9 μsec, with a peak-to-minimum ratio of 12,400 and with 80% of the power in the pulse. These pulses, when thermalized by the scatterer, were broadened to a width at half-maximum of 20.9 μsec with a peak-to-minimum power ratio of 1590. The number of thermal neutrons leaking from the outer surface of the scatterer was 3.3 × 10−5 n/(cm2 fission).