Rare earth elements natural radioactivity

The silver gray metal can be cut with a knife, although it only melts at 1545 °C (for comparison, iron 1538 °C). It is the rarest of the "rare earths", but is nevertheless more abundant than iodine, mercury, and silver. Thulium has few applications, especially because it is relatively expensive. The element occurs naturally as a single isotope, namely 169Tm (compare bismuth). The artificial, radioactive 170Tm is a transportable source of X-rays for testing materials. Occasionally used in laser optics and microwave technology. 

These two long rows of elements are traditionally moved to the base of the chart so the more important, lighter elements may be closer together for clarity. These two rows of metals each reflect the progressive addition of 14 electrons into an /-type subshell. The lanthanides occur in only trace amounts in nature and are often called rare earths. All of the actinides have large, unstable nuclei that undergo spontaneous radioactive decay. 

Linsalata P, Penna Franca E, Sachett I, et al. 1987. Radium, thorium, and the light rare earth elements in soils and vegetables grown in an area of high natural radioactivity. DOE Symp Ser 59 131-146. 

G. Hevesy and H. Levi, Artificial radioactivity of dysprosium and other rare earth elements, Nature 136 (1935) 103. G. Hevesy and H. Levi, Action of slow neutrons on rare earth elements, Nature 137 (1936) 185. 

Promethium is a radioactive element with a half-life of 2.6 years and does not occur naturally. The other elements, known sometimes as the rare earth elements, are always found in association, principally in the minerals monazite (LnP04) and bastneasite (LnC03F). The electropositive and reactive elements can be obtained by reduction of LnCl3 with Ca, and are sometimes used together as mischmeta. Specialist... 

The last element of the group of metalloids is astatine. It has been estimated that the whole Earth s crust contains less than 44 mg astatine and this element with the atomic number 85 can thus be considered one of the rarest naturally occurring elements on Earth. All isotopes of this radioactive element have short half-lives and are products of several radioactive decay series. At (ti/2 = 54 s) occurs in one rare side branch of the decay series while At, one of the products of a side branch of the Po decay series, undergoes a very fast P decay (ti/2 = IxlO s). 

The element is named after Thule, the ancient name for Scandinavia. It is part of the yttria rare earths and is about as abundant as silver or cadmium. It was discovered in 1879 by Per Theodor Cleve. The silvery metallic element does not occur in elemental form naturally. It is very expensive and has few commercial uses, although synthetic radioactive isotopes have been used as an X-ray source. 

Millions of simple and complex substances are found in nature or produced in the chemical laboratory, but the total number of elements that combine to form these substances is much, much smaller. By the year 2003, 114 elements had been discovered, but 24 of these elements are not found naturally on the earth, and chemists do not generally work with them. Of these 24 elements, 2 or 3 might exist in stars, but the rest are not thought to exist outside the physicist s laboratory. (See Special Topic 2.1 Why Create New ElementsTj Some of the elements found in nature are unstable that is, they exist for a limited time and then turn into other elements in a process called radioactive decay. Of the 83 stable elements found in nature, many are rare and will not be mentioned in this text. The most important elements for our purposes are listed on Table 2.1. 

Promethium. Pm at. wt of best known isotope 147 at. no. 61 valence 3. All known isotopes are radioactive mass numbers 140-154. M7Pm, a 0-emitter, T, 2.62 years. The discovery of element 61 in rare earth concentrate was claimed by Harris and Hopkins, J, Am. Chem. Soc. 48, 1585 (1926) and by Rolla and Fernandez, Gazz. Chim. ItaL 56, 435 (1926). Evidence of existence in nature is inconclusive Yost et ah. The Rare Earth Elements and Their Compounds (John Wiley, New York, 1947). First obtained synthetically by irradiating neodymium and praseodymium with neutrons, deuterons, and alpha particles Law et at., Phys. Rev. 59, 936 (1941). Positive identification by inn-exchange chromatography Marinsky et ah, J. Am. Chem. Soc. 69,... 

Thulium, Tm at. wt 168.9342 at. no. 69 valence 3- A rare earth element of the yttrium group. One naturally occurring isotope ltsTm artificial, radioactive isotopes ... 

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