Second Report on Propulsion by a Gaseous Fission Reactor.
A continuation of the reexamination of gaseous fission reactors begun in RM-3769. It has been pointed out that the neutron temperature will be somewhat higher than that of the D20 reflector (considered in RM-3769), since there is on the order of a scattering mean free path of hot deuterium in the reactor core. It has also been noted that structural poisons will further increase the critical mass. The present memorandum continues by taking into account another effect, which is even more serious in increasing the critical mass--i.e., the decrease in neutron mean free path due to the thermal motion of the deuterons.