Actinium abundance

As the parent of actinium in this series it was named protoactinium, shortened in 1949 to protactinium. Because of its low natural abundance its chemistry was obscure until 1960 when A. G. Maddock and co-workers at the UK Atomic Energy Authority worked up about 130g from 60 tons of sludge which had accumulated during the extraction of uranium from UO2 ores. It is from this sample, distributed to numerous laboratories throughout the world, that the bulk of our knowledge of the element s chemistry was gleaned. 

The actual situation with regard to the purity of most of the actinide metals is far from ideal. Only thorixun (99), uranium 11,17), neptunium 20), and plutonium 60) have been produced at a purity > 99.9 at %. Due to the many grams required for preparation and for accurate analysis, it is probable that these abundant and relatively inexpensive elements (Table I) are the only ones whose metals can be prepared and refined to give such high purities, and whose purity can be verified by accurate analysis. The purity levels achieved for some of the actinide metals are listed in Table II. For actinium (Ac), berkelium (Bk), californium (Cf),... 

Ac, actinium, was initially identified in 1899 by Andr6-Louis Debierne, a French chemist, who separated it from pitchblende. He dissolved the mineral in acid, then added NH4OH, and found that a radioactive species was carried down with the rare earth hydroxides. He named the element actinium after the Greek aktinos which means ray. Because of its low abundance in U, the element is usually not obtained by isolation from U. It can be obtained in mlligram amounts by irradiation of Ra-226 in a nuclear reactor. The preparation of Ac metal involves reduction of AcFs by Li at high temperature. 

The alkali metals are not found free in nature, because they are so easily oxidized. They are most economically produced by electrolysis of their molten salts. Sodium (2.6% abundance by mass) and potassium (2.4% abundance) are very common in the earth s crust. The other lA metals are quite rare. Francium consists only of short-lived radioactive isotopes formed by alpha-particle emission from actinium (Section 26-4). Both potassium and cesium also have natural radioisotopes. Potassium-40 is important in the potassium-argon radioactive decay method of dating ancient objects (Section 26-12). The properties of the alkali metals vary regularly as the group is descended (Table 23-1). 

Related topics Actinium and the actinides (12) Origin and abundance of the elements (J1)... 

An asterisk denotes a radioactive isotope whose lifetime is indicated in the column Natural abundance. When a stable element has several radioactive isotopes, a few ones have been chosen for their interest in different applications. For the radioactive elements, only the isotopes with the longest lifetimes and at least one with a nonzero nuclear spin I are indicated. The electronic configuration of an element with atomic number Z is given in italics in the Name and symbol column. When relevant, the old Group label notation of the periodic table is indicated in brackets in this same column. The radioactive elements francium, radium, and actinium (Z = 87, 88, and 89, respectively) have been omitted. 

FlC- 1-2, The three naturally occurring radioactive decay series and the man-made neptunium series. Although (which is the parent to the actinium series) and (which is the parent to the thorium series) have been discovered in nature, die decay series shown here begin with the most abundant Icmg-Uved nuclides. 

We have already discussed the history of discovery of two natural radioactive elements, that is, uranium and thorium, in Chapter 4. These elements can fairly easily be found in minerals with chemical analysis since their content is sufficiently high. Other natural radioactive elements (polonium, radon, radium, actinium, and protactinium) are among the least abundant elements on Earth. Moreover, they exist in nature only because they are the products of radioactive transformations of uranium and thorium. 

Actinium was discovered by A. Debierne in 1899. Its name is derived from the Greek word for beam or ray, referring to its radioactivity. The natural occurrence of the longest lived actinium isotope Ac, with a half-life of 21.77 years, is entirely dependent on that of its primordial ancestor, U. The natural abundance of Ac is estimated to be 5.7 10 ppm. The most concentrated actinium sample ever prepared from a natural raw material consisted of about 7 fig of Ac in less than 0.1 mg of... 

As Table 21.1 indicates, the group 1 elements, the alkali metals, are relatively abundant. Some of their compounds have been known and used since prehistoric times. Yet these elements were not isolated in pure form until about 200 years ago. The compounds of the alkali metals are difficult to decompose by ordinary chemical means, so discovery of the elements had to await new scientific developments. Sodium (1807) and potassium (1807) were discovered through electrolysis. Lithium was discovered in 1817. Cesium (1860) and rubidium (1861) were identified as new elements through their emission spectra. Francium (1939) was isolated in the radioactive decay products of actinium. 

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