322 | The History and Use of Our Earth’s Chemical Elements Abundance฀and฀Source

322 | The History and Use of Our Earth’s Chemical Elements Abundance฀and฀Source

Americium does not exist in nature. All of its isotopes are man-made and radioactive. Americium-241 is produced by bombarding plutonium-239 with high-energy neutrons, resulting in the isotope plutonium-240 that again is bombarded with neutrons and results in the formation of plutonium-241, which in turn finally decays into americium-241 by the process of beta decay. Both americium-241 and americium-243 are produced within nuclear reactors. The reaction is as follows: 239 Pu + (neutron and λ gamma rays) → 240 Pu + (neutron

and λ gamma rays) → 241 Pu→ 241 Am + beta minus (β-); followed by 241 Am→ 93 Np-237 +

4 He

2 (helium nuclei). History At the end of World War II, the American physicists Glenn T. Seaborg (1912–1999), Ralph

A. James, Leon O. Morgan, and Albert Ghiorso discovered americium (and curium) in the Metallurgical Laboratory at the University of Chicago, now known as the Argonne National Laboratory. The element curium ( 96 Cm) was first discovered as they bombarded plutonium with high-speed neutrons. This event was followed by the detection of the element americium ( 95 Am). These two elements were discovered in reverse order in 1944, but they both fell into place for the transuranic subseries elements of the actinide series. Although finding new ele- ments is one thing, positively identifying their chemical and physical properties to the satis- faction of other scientists as “new” and fitting the periodic table is another. It required some effort and time for the team to identify all the properties and characteristics of curium and americium, which led a wag to suggest the names “pandemonium” and “delirium” for the two new elements because of the difficulties the team had in the confirmation of their identities.

Common฀Uses Americium-141, with a half-life of 432 years, which produces both alpha (helium nuclei)

and gamma rays (somewhat like X-rays), has found some commercial uses. One use is as the detector used in household smoke alarms The americium-141 isotope emits alpha particles that ionize air by removing electrons from the molecules of air and improving its electrical conductivity. Smoke reduces this conductivity, thus triggering the alarm. Another use is ameri- cium-241’s high-energy gamma rays in radiography, in which portable X-ray instruments can easily be transported for emergency use. As a gamma ray source, americium-241 is used as a diagnostic aid to check the quality of welds in metals.

Examples฀of฀Compounds Only a few compounds of americium exist. The most important is americium oxide

(AmO 2 ), whose main use is in the preparation of other compounds. Americium can also form compounds with the halogens, similar to other transuranic elements—for example, americium iodide (AmI 3 ), americium fluoride, and americium chloride (AmF 3 and AmCl 3 ).

Hazards All the isotopes and compounds of americium are deadly sources of radiation and cause

radiation poisoning and death. Precautions must be taken when working with it. The small amount of americium-241 found in smoke detectors in household smoke alarms is harmless unless the isotope is removed and swallowed.

323 CURIUM

Guide to the Elements |

SYMBOL:฀Cm฀ PERIOD:฀7฀ SERIES฀NAME:฀Actinides฀ ATOMIC฀NO:฀96 ATOMIC฀MASS:฀247฀amu฀ VALENCE:฀3฀and฀4฀ OXIDATION฀STATE:฀+3฀and฀+4฀ NATU-

RAL฀STATE:฀Solid ORIGIN฀OF฀NAME:฀Named฀after฀Pierre฀and฀Marie฀Curie. ISOTOPES:฀There฀are฀23฀isotopes฀of฀curium.฀All฀of฀them฀are฀man-made฀and฀radioactive.฀

The฀most฀stable฀is฀curium-247,฀with฀a฀half-life฀of฀1.56×10 +7 years฀(156,600,000฀years),฀ which฀through฀alpha฀decay฀transmutates฀into฀plutonium-243.

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

s2,฀p6

฀ 3-M฀=฀18฀

s2,฀p6,฀d10

฀ 4-N฀=฀32฀

s2,฀p6,฀d10,฀f14

฀ 5-O฀=฀25฀