Earnshaw Medal
Earnshaw 2009 Nominees: Ronan Rochford, NUIG
Computational estimation of the critical mass of a Nuclear Fission weapon
Nuclear testing is a dangerous process and can cause numerous environmental problems. For this reason scientists have sought to find an accurate computational method for testing nuclear weapons. The aim of this project was to computationally estimate the critical mass of a nuclear fission weapon. This is dependent on the design of the weapon and the properties of the fissile material. The shape, purity, neutron mean path and use of a tamper can all significantly alter the critical mass. The simulation was tackled with a C environment with a Monte Carlo design. The code was written in a spatial manner, as it followed each neutron individually through the process. The code included aspects such as impurity levels, tampers, accuracy levels and original fissions. It was also possible to follow the neutron interactions in 3-D.
The results were highly accurate giving values of 52.25kg and 15.67kg for 235U without and with tamper, respectively. The expected values were » 52kg and » 15kg. Results for 239Pu values of » 9.83kg and 4.94kg without and with tamper respectively. The expected values were » 10kg and» 5kg. The results obtained show that critical mass cannot be obtained below a purity level of 40%, without more modifications.
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