a device in which a quantity of fissionable material, less than a critical mass, has its volume suddenly decreased by compression, so that it becomes supercritical and an explosion can take place, seade mingi kriitilisest massist väiksema hulga lõhestumiskõlbuliku materjaliga, mille mahtu kokkusurumise teel järsku vähendatakse nii, et see muutub ülekriitiliseks ja toimub plahvatus