| americium | (n) a radioactive transuranic metallic element; discovered by bombarding uranium with helium atoms, Syn. atomic number 95, Am |
| berkelium | (n) a radioactive transuranic element; discovered by bombarding americium with helium, Syn. atomic number 97, Bk |
| californium | (n) a radioactive transuranic element; discovered by bombarding curium with alpha particles, Syn. atomic number 98, Cf |
| curium | (n) a radioactive transuranic metallic element; produced by bombarding plutonium with helium nuclei, Syn. atomic number 96, Cm |
| einsteinium | (n) a radioactive transuranic element produced by bombarding plutonium with neutrons, Syn. Es, atomic number 99, E |
| fluorine | (n) a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite, Syn. atomic number 9, F |
| neptunium | (n) a radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium, Syn. Np, atomic number 93 |
| plutonium | (n) a solid silvery grey radioactive transuranic element whose atoms can be split when bombarded with neutrons; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known with the most important being plutonium 239, Syn. atomic number 94, Pu |
| protactinium | (n) a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead, Syn. protoactinium, atomic number 91, Pa |
| thorium | (n) a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands, Syn. Th, atomic number 90 |
| uranium | (n) a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons, Syn. U, atomic number 92 |
