Note on the minimum critical mass for a tamped fission bomb core

摘要

An approximate but sensibly accurate formula is developed for estimating the minimum possible critical radius for a sphere of fissile material surrounded by a thick tamper of material of neutron transport mean free path lambda(tamp). The minimum critical radius is approximately proportional to lambda(0.4)(tamp); results are given for uranium-235 and plutonium-239 cores surrounded by several commonly used tamper materials. (C) 2015 American Association of Physics Teachers.