320 | The History and Use of Our Earth’s Chemical Elements History

320 | The History and Use of Our Earth’s Chemical Elements History

The discovery and early use of plutonium is a unique story. In 1941 Glenn T. Seaborg (1912–1999) and his colleagues, Arthur Wahl (1917–2006) and Joseph Kennedy (1915– 1956) , found trace amounts (about 1 gram) of plutonium ( 94 Pu) in neptunium ( 93 Np) at the physics labs of the University of California at Berkeley. They used the university’s cyclotron to produce plutonium by bombarding uranium oxide with deuterons (nuclei of heavy hydro- gen), which first produced neptunium that decayed into plutonium as it gained a proton that increased its atomic number to 94. They recorded their discovery but did not publish it until 1946 because of World War II. Once plutonium was determined to be fissionable and once it was seen that a critical mass of the element could maintain a sustained chain reaction, it was “classified.” A large factory was constructed to produce kilogram quantities of this new element that required several kilograms less than the fissionable but scarce uranium-235 to build atomic (nuclear) bombs. This mass production of the newly discovered plutonium and its use in early atomic weapons became a reality years before most scientists and the public knew it even existed. Today, plutonium is a by-product of the operations of nuclear power reactors, and there is an excess of it to the point that how to store this extremely radioactive waste product has become problematic. Scientists have yet to discover a way to make pluto- nium in a stable form, and they are still studying the strange properties and characteristics of this artificially produced element.

Common฀Uses The most common use of plutonium is as a fuel in nuclear reactors to produce electricity or

as a source for the critical mass required to sustain a fission chain reaction to produce nuclear weapons. Plutonium also is used to convert nonfissionable uranium-238 into the isotope capable of sustaining a controlled nuclear chain reaction in nuclear power plants. It takes only 10 pounds of plutonium-239 to reach a critical mass and cause a nuclear explosion, as compared with about 33 pounds of fissionable, but scarce, uranium-235.

Plutonium-238 and plutonium-239 are two isotopes that can be used outside of the nuclear weapons industry. Plutonum-238 is currently used in small thermoelectric generators to provide electricity for space probes that are sent far beyond the region where the sun could

be used to generate electric power. Two early instruments sent beyond our solar system are the Galileo and Cassini probes. Plutonium-239’s critical mass undergoes a fissionable chain reaction, making it ideal for use as fuel for some types of nuclear reactors as well as to produce nuclear weapons. In the future it may be possible to use all the waste plutonium produced in the world to power small thermal electrical power plants that could be installed in each house to provide inexpensive and continuous household electrical power. This probably will not happen until the public overcomes its fear of nuclear energy.

Examples฀of฀Compounds Plutonium can form compounds with many nonmetals such as oxygen, the halogens, and

nitrogen. It can also be used as an alloy with other metals. A few examples of plutonium com- pounds exhibiting the oxidation states of +3 and +4 follow:

Plutonium (III) fluoride: Pu 3+ + 3F 1- → PuF 3 . Also called plutonium trifluoride. Plutonium (IV) oxide: Pu 4+ + 2O 2- → PuO 2 . Also known as plutonium dioxide.

321 Hazards

Guide to the Elements |

Plutonium is by far one of the most toxic radioactive poisons known. The metal, its alloys, and its compounds must be handled in a shielded and enclosed “glove box” that contains an inert argon atmosphere. It is a carcinogen that can cause radiation poisoning leading to death.

AMERICIUM SYMBOL:฀Am฀ PERIOD:฀7฀ SERIES฀NAME:฀Actinide฀ ATOMIC฀NO:฀95

ATOMIC฀MASS:฀243฀amu฀ VALENCE:฀3,฀4,฀5,฀and฀6฀ OXIDATION฀STATE:฀+3,฀+4,฀+5฀and฀ +6฀ NATURAL฀STATE:฀Solid

ORIGIN฀OF฀NAME:฀Named฀after฀the฀continent฀America฀because฀Europium฀was฀named฀ after฀the฀European฀continent.

ISOTOPES:฀There฀are฀24฀isotopes฀of฀americium.฀All฀are฀radioactive฀with฀half-lives฀ranging฀ from฀72฀microseconds฀to฀over฀7,000฀years.฀Five฀of฀americium’s฀isotopes฀are฀fissionable฀

with฀spontaneous฀alpha฀decay.

ELECTRON฀CONFIGURATION ฀ Energy฀Levels/Shells/Electrons฀ Orbitals/Electrons