Project Y: the Los Alamos Story - David Hawkins
David Hawkins - Project Y: the Los Alamos Story, p.188.
The gloomy prospects for implosion in the fall and winter of 1944-45 made it desirable again to investigate autocatalytic and otht possible methods of weapon assembly. This whole subject had been investigated earlier and given up because of the uniformly low efficiencies indicated. Autocatalysis makes use of neutron absorbers removed in the course of the initial explosion. Therefore, one or more paraffin spheres coated with B-10 may be placed inside the fissionable material so that the whole assembly is just subcritical. If a chain reaction is started, heating of the material compresses boron "bubbles," reduces the neutron absorbing area, and increases the degree of criticality. Thus, in principle, the progress of the explosion creates conditions favorable to its further progress. Unfortunately, the autocatalytic effect is not large enough to compensate for the poor initial conditions of this type of explosion and the result is not impressive.
Another type of assembly mechanism examined made use of shaped charges to attain much higher velocities of a slug of active material than would be possible with conventional gun mechanisms. This method also gave low efficiency when calculated for the high-neutron background of Hanford plutonium.
The gloomy prospects for implosion in the fall and winter of 1944-45 made it desirable again to investigate autocatalytic and otht possible methods of weapon assembly. This whole subject had been investigated earlier and given up because of the uniformly low efficiencies indicated. Autocatalysis makes use of neutron absorbers removed in the course of the initial explosion. Therefore, one or more paraffin spheres coated with B-10 may be placed inside the fissionable material so that the whole assembly is just subcritical. If a chain reaction is started, heating of the material compresses boron "bubbles," reduces the neutron absorbing area, and increases the degree of criticality. Thus, in principle, the progress of the explosion creates conditions favorable to its further progress. Unfortunately, the autocatalytic effect is not large enough to compensate for the poor initial conditions of this type of explosion and the result is not impressive.
Another type of assembly mechanism examined made use of shaped charges to attain much higher velocities of a slug of active material than would be possible with conventional gun mechanisms. This method also gave low efficiency when calculated for the high-neutron background of Hanford plutonium.