Actinium-227

Actinium-227 occurs in uranium ore and is a decay product of uranium-235. It is found in equilibrium with its decay products. It is prepared hy homhard-ing radium atoms with neutrons. Chemically, the metal is produced hy reducing actinium fluoride with lithium vapor at 1,100°C to 1,300°C. 

The element was discovered independently hy A. Dehierne and F. Giesel in 1899 and 1902, respectively. It is used in nuclear reactors as a source of neutrons. 

Silvery metal cubic crystal melts at 1,051°C vaporizes at 3,198°C density 10.0 g/cm3 

The radioactivity can be measured by a beta counter. The metal at trace concentrations can be determined by an atomic absorption or emission spectrophotometer. 

Actinium forms halides only in the (+3) oxidation state, AcXs and AcOX (X = F, Cl, Br). The trihalides have the LaFs (X = F) and UCI3 (X = Cl, Br) structures, respectively. 

All isotopes of actinium are radioactive and exist in aqueous solution only in the trivalent state. All of the isotopes of actinium are relatively short lived, with the longest half-life being 21.6 years for Ac. Consequently, it is difficult to measure the stability of its aqueous species or the solubility of its phases. 

The chemical behaviour of actinium will be similar to that of lanthanum. Data are only available for two monomeric hydrolysis species and the solubility of the hydroxide phase. The solubility of this phase can be described by reaction (2.13) (M = Ac, x = 0), whereas the hydrolysis constants can be described by reaction (2.5) (M = = 1) for actinium(lll) in reaction (2.5),, the number of hydrox- 

ORIGIN OF NAME The name actinium is derived from the Greek word(s) aktis or akti-nos, meaning beam or ray.  

ISOTOPES There are a total of 35 isotopes of actinium, none of which are stable. All are radioactive, and none exist in the Earth s crust in any large amounts, although a few can be extracted from large quantities of pitchblende and other minerals. All are extremely scarce. Those produced artificially in nuclear reactors, cyclotrons, or linear accelerators have relatively short half-lives, ranging from 69 nanoseconds to 21 years. 

Energy Levels/Shells/Electrons Orbitals/Electrons 

Actinium is an extremely radioactive, silvery-white, heavy metal that glows in the dark with an eerie bluish hght. It decays rapidly which makes it difficult to study, given that it changes into thorium and francium through electron capmre and alpha decay. Its melting point is 1,051°C, its boding point is 3,198°C, and its density is 10.07g/cm.  

Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic table and the first of the actinide series of metallic elements that share similar chemical and physical characteristics. Actinium is also closely related in its characteristics to the element lanthanum, which is located just above it in group 3. The elements in this series range from atomic number 89 (actinium) through 103 (lawrencium). Actiniums most stable isotope is actinium-227, with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 through beta decay, and both of these isotopes are decay products from uranium-235. 

Cotton, Simon (1991). Lanthanides and Actinides. New York Oxford University Press. 

In 1945 Glenn Seaborg proposed that actinium was the first member of a family of fifteen elements (the actinides ), characterized by the possession of the 5/orbitals. His proposal was based on the similarity of the chemistry of actinium to that of lanthanum (atomic number 57), which is the first member of the fifteen elements of the trivalent lanthanide family. Actinium is somewhat more basic than lanthanum but, like lanthanum, forms compounds that have strongly ionic bonds. Many actinium compounds are 

Was it just a chance that polonium and radium were the first to be discovered among radioactive elements The answer is apparently no. Owing to its long half-life radium can be accumulated in uranium ores. Polonium has a short half-life (138 days) but it emits characteristic high-intensity alpha radiation. Though the discovery of polonium gave rise to a controversy it soon died off. 

The third success of the young science of radioactivity was the discovery of actinium. Soon after they had discovered radium the Curies suggested that uranium ore could contain other, still unknown radioactive elements. They entrusted their collaborator A. Dehierne with verification of this idea. 

Dehierne started his work with a few hundreds kilograms of uranium ore extracting the active principle from it. After, he had extracted uranium, radium, and polonium he was left with a small amount of a substance whose activity was much higher than the activity of uranium (approximately, by a factor of 100 000). At first, Dehierne assumed that this highly radioactive substance was similar to titanium in its chemical properties. Then he corrected himself and suggested a similarity with thorium. Later, in spring of 1899 he announced the discovery of a new element and called it actinium (from the Greek for radiation). 

Any textbook, reference book or encyclopedia gives 1899 as the date of the discovery of actinium. But in fact, to say that in 1899 Dehierne discovered a new radioactive element— actinium—means to ignore very significant evidence to the contrary. 

The real actinium has little in common with thorium but we did not mean this chemical difference as evidence against the discovery of actinium by Dehierne. The main argument is as follows. Dehierne believed that actinium was alpha-active and its activity was 100 000 times that of uranium. Now we know that actinium is a mild beta-emitter, that is, it emits beta rays of a fairly low energy which are not that easy to detect. Of course, the primitive radiometric apparatus of Dehierne was not capable of doing it. 

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Ac Actinium. Also used for acetate (ethan-oate). 

Twenty isotopes are known. Radon-22, from radium, has a half-life of 3.823 days and is an alpha emitter Radon-220, emanating naturally from thorium and called thoron, has a half-life of 55.6 s and is also an alpha emitter. Radon-219 emanates from actinium and is called actinon. It has a half-life of 3.96 s and is also an alpha emitter. It is estimated that every square mile of soil to a depth of 6 inches contains about 1 g of radium, which releases radon in tiny amounts into the atmosphere. Radon is present in some spring waters, such as those at Hot Springs, Arkansas. 

Care must be taken in handling radon, as with other radioactive materials. The main hazard is from inhalation of the element and its solid daughters which are collected on dust in the air. Good ventilation should be provided where radium, thorium, or actinium is stored to prevent build-up of the element. Radon build-up is a health consideration in uranium mines. Recently radon build-up in homes has been a concern. Many deaths from lung cancer are caused by radon exposure. In the U.S. it is recommended that remedial action be taken if the air in homes exceeds 4 pCi/1. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

Fig. 5a. Standard (or formal) reduction potentials of actinium and the actinide ions in acidic (pH 0) and basic (pH 14) aqueous solutions (values are in volts...

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

With the exception of actinium, which is found naturally only in traces in uranium ores, these elements are by no means rare though they were once thought to be so Sc 25, Y 31, La 35 ppm of the earth s crustal rocks, (cf. Co 29ppm). This was, no doubt, at least partly because of the considerable difficulty experienced in separating them from other constituent rare earths. As might be expected for class-a metals, in most of their minerals they are associated with oxoanions such as phosphate, silicate and to a lesser extent carbonate. 

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