These are actinides other than uranium and plutonium and include neptunium, americium and curium. Berkelium was the fifth transuranium element discovered after neptunium, plutonium, curium and americium. This criterion includes plutonium, uranium, americium, and neptunium among others. Seaborg developed the chemical elements americium and curium while in Chicago. Other fission products remain in the aqueous phase, including americium and curium. Similar conclusion was drawn for other actinides americium, berkelium and fermium. The discoveries of americium, berkelium, and californium followed soon. Its toxicity is comparable to, but slightly lower than that of americium and plutonium. Metallic americium is obtained by reduction from its compounds. The pentavalent oxidation state of americium was first observed in 1951. The most stable oxidation state for americium is +3. A large amount of work has been done on the solvent extraction of americium. The crystal structure of americium changes with pressure and temperature. His intention was to obtain americium from them.