All Federation starships were equipped with Bussard collectors, which were optimally positioned to collect interstellar particles. Collection worked best in regions where particle density was high, such as in star systems or nebulae. The Bussard collector normally collected hydrogen, especially deuterium, for fuel replenishment, but could be reconfigured to collect various gases like sirillium and plasma particles. A Bussard collector could also be reconfigured to expel gases or plasma. (TNG: "Samaritan Snare" ) Bussard collectors were not capable of producing nadion emissions. (VOY: "The Haunting of Deck Twelve")