Title: Simulating an Exploding Fission-Bomb Core with a Desktop Computer

Abstract:

This colloquium will describe a program developed for a desktop computer which carries out a time-dependent simulation of the core of an exploding nuclear weapon. The logic of the program is understandable to any student familiar with kinematics and vectors; the necessary nuclear concepts will be introduced as needed. The simulation models a core comprising a mixture of two isotopes: A fissile one (such as uranium-235) and an inert one (such as uranium-238) that captures neutrons and removes them from circulation. The user sets the enrichment percentage and properties of the fissile isotope, the capture probability of the inert isotope, the number of neutrons liberated per fission, the number of “initiator” neutrons, the radius of the core, and the neutron-reflection efficiency of a surrounding tamper. The simulation then follows the three-dimensional motions and fates of neutrons as they travel through the core. Limitations of time and memory render impossible attempting to model a real-life core, but results of numerous runs clearly demonstrate the existence of a critical core radius for a given set of parameters and the dramatic effects of enrichment and tamper efficiency on the growth (or decay) of the neutron population. The logic of the simulation will be described and results of typical runs will be presented and discussed.