Americium, 433 Atomic number

Radioactive substances also have life-saving uses. A radioactive form of cobalt is extensively used in radiation therapy for cancer patients. The treatment was first developed by Harold Johns (1915—) in Canada, where he pioneered cobalt therapy units at the University of Saskatchewan. One of the artificially made elements, Americium (atomic number 95, i.e., with 95 protons in its atomic nucleus), is another life-saving radioactive element. As it decays, it emits alpha particles, which strip electrons from surrounding gas molecules ionized air conducts electricity much better than air containing smoke particles, and the reduction in conductivity produced by smoke is what triggers the alarm in smoke detectors. 

Chemical studies show it to have properties very similar to uranium and neptunium but the lower cixidation states are rnon stable. Americium, atomic number 95, was the fourth transuranium element obtained. The reactions taking place on the bombardment of U by high energy... 

Seaborg GT, James RA, Morgan LO (1949a) The new element americium (atomic number 95). In Seaborg GT, Katz JJ, Manning WM (eds) The transuranium elements, research papers n. McGraw-Hill, New York, pp 1525-1553... 

Leboeuf, Miller, and Connally5 have carried out an extensive investigation of 7-ray absorptiometry with several sources (notably an americium-plutonium mixture) not listed in Table 11-2. These authors were in an exceptionally favorable position to compare 7-ray and x-ray absorptiometry on highly absorbing samples (usually high both in mass and in atomic number). The following is a summary of their comparison. 

Americium (pronounced,, am-8- ris(h)-e-8m) is a man-made, radioactive, actinide element with an atomic number of 95. It was discovered in 1945. Actinides are the 15 elements, all of whose isotopes are radioactive starting with actinium (atomic number 89), and extending to lawrencium (atomic number 103). When not combined with other elements, americium is a silvery metal. Americium has no naturally occurring or stable isotopes. There are two important isotopes of... 

Americium - the atomic number is 95 and the chemical symbol is Am. The name derives from America where it was first synthesized in a series of successive neutron capture reactions in the element plutonium, Pu, in a nuclear reactor in 1944 by American scientists under Glenn T. Seaborg at the University of California lab in Berkeley, California, using the nuclear reaction Pu ( n, y) Y) P Am. Americium is the sixth element in the Actinide... 

The pure metal of berkelium does not exist in nature and has never been directly artificially produced, although the first isotope of berkelium produced was berkelium-243. It was artificially formed by bombarding americium-241 with the nuclei of helium (alpha particles), as follows " Am+lalpha particle = 2 protons + 2 neutron)—> Bk. (Note Two protons as well as two neutrons are found in the nucleus of helium, and thus the two protons changed the atomic number of americium [ jAm] to berkelium [j Bk].) Today a different process is used to produce berkelium in small amounts, as follows Cm+(5n = neutrons X = gamma rays) —> (becomes) —> Bk + P- = (beta-minus decay). 

TRANSACTINIUM EARTHS. A group of chemical elements more frequently termed the Actinides. In order of increasing atomic number, they indude actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium. and lawrencium. See also Actinide Contraction. 

Transuranic waste that contains plutonium, americium, and other elements with atomic numbers higher than uranium... 

Usually the discovery of a new element is announced in a scientific paper or at a scientific meeting. The actinide elements curium and americium were announced to the world in a 1945 childrens radio show called Quiz Kids. The show s guest scientist on November 11 that year was a young scientist named Glenn Seaborg. One of the children on the show asked Seaborg if any new elements had been discovered lately. Seaborg happily shared the news that his lab had in fact created two new elements with atomic numbers 95 and 96. 

The difference in the chemistry of the light and heavy actinides may be rationalized in this way. The early members beyond thorium have unpaired d and / electrons available for forming covalent bonds and hence, for example, they readily form many complex ions and intermetallic compounds. Such ions are soft acids. Beyond americium, the 5/ electrons are not competitive and the closed shell of six 5/5/2 electrons will not be readily available for bonding, so that only those / electrons with /=7/2 are available. These tend to become buried radially as the atomic number increases and hence their divalent ions become relatively hard Lewis acids. These considerations are especially helpful in the region of superactinides because these elements do not have analogs in the known periodic table, where we have deeply buried but loosely bound 5g electrons. 

Americium is called an actinoid or transuranium element. It occurs in Row 7 of the periodic table, a chart that shows how the chemical elements are related to each other. The actinoids are named after element 89, actinium. The term transuranium means beyond uranium in the periodic table. Uranium has an atomic number of 92. Any element with an atomic number larger than 92, therefore, is called a transuranium element. 

The UCB researchers fired alpha particles—helium atoms without their electrons—at americium atoms in their particle accelerator. The result was a new element—number 97. 

Actinide series Actinides are radioactive elements. Only three actinides exist in nature. The rest are synthetic elements called transuranium elements. A transuranium element is an element whose atomic number is greater than 92, the atomic number of uranium. Transuranium elements are created in particle accelerators or nuclear reactors. Most transuranium elements decay quickly. One notable exception is plutonium-239. A sample of this isotope can remain radioactive for thousands of years. Plutonium is used as a fuel in nuclear power plants. The home smoke detector in Figure 7-27b uses americium. 

Between hydrogen and uranium a maximum number of 90 elements is indicated and all of these are known to occur in Nature with the exception, possibly, of elements 61, 85 and 87. The search for an element of higher atomic number than uranium for long proved abortive indeed theoretical reasons were adduced to show that such an element would be too unstable to exist more than momentarily. But elements 93 (neptunium) and 94 (plutonium) are now known to occur in Nature they have also been synthesised together with 95 (americium) and 96 (curium). ... 

Successive neutron capture in Pu (as occurs in nuclear reactors) produces isotopes of plutonium which undergo 0 -decay, forming transplutonium elements with atomic numbers 95 (americium) and 96 (curium) (Fig. 16.2). The reaction sequence is... 

Beta particles are charged particles emitted from the nucleus of an atom with a mass and charge equal in magnitude to that of an electron. In beta decay reactions, as the electron is ejected, the number of protons in the resulting atom increases, changing the atomic number of the atom but not the mass. For example, plutonium-241 undergoes beta decay to form americium-241. 

Elements with atomic numbers higher than that of uranium, 92, called transuranium elements, have been obtained artificially from 1940, and all are radioactive many isotopes of each are known. They are formed by bombarding ordinary uranium, or themselves, with neutrons, or high-energy helium ions He2+, and are called neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Mv), nobelium (No), and lawrencium, with atomic numbers from 93 to 103, respectively. Details must be sought elsewhere. ... 

Americium has the atomic number 95 and the valence electrons are on the 5f shell. Half life of Am is 462 years. 

Americium and curium were placed after actinium in the actinide series in the Periodic Table because their chemical properties were similar. Since that time, elements with atomic numbers to 118 have been reported by scientists around the world. 

J3AI + Jn iiNa + pie represents the bombardment of aluminum with neutrons to produce an isotope of sodium and helium nuclei (alpha particles). All transuranic elements above curium, atomic number 96, are artificially radioactive because they do not occur in nature. Even neptunium, plutonium, americium. 

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