Conducting an experiment that combines high explosives with plutonium—a special nuclear material used in nuclear weapons—is no trivial matter. Not only do researchers need to ensure the plutonium remains “subcritical” to avoid a nuclear explosion, they must be absolutely certain that these materials are confined in a worst-case scenario. On top of that, they have to be sure they can collect data they need to continue to ensure the safety, security and effectiveness of the U.S. nuclear stockpile.