Protactinium elements

Before it was known that elements beyond uranium were capable of existence, the heaviest known natural elements, thorium, protactinium and uranium, were placed in a sixth period of the periodic classification, corresponding to the elements hafnium, tantalum and tungsten in the preceding period. It was therefore implied that these elements were the beginning of a new, fourth transition series, with filling of the penultimate n = 6 level (just as the penultimate = 5... 

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. 

The actinide elements exhibit uniformity in ionic types. In acidic aqueous solution, there are four types of cations, and these and their colors are hsted in Table 5 (12—14,17). The open spaces indicate that the corresponding oxidation states do not exist in aqueous solution. The wide variety of colors exhibited by actinide ions is characteristic of transition series of elements. In general, protactinium(V) polymerizes and precipitates readily in aqueous solution and it seems unlikely that ionic forms ate present in such solutions. 

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). 

Prior to 1940 only the naturally occurring actinides (thorium, protactinium and uranium) were known the remainder have been produced artificially since then. The transactinides are still being synthesized and so far the nine elements with atomic numbers 104-112 have been reliably established. Indeed, the 20 manmade transuranium elements together with technetium and promethium now constitute one-fifth of all the known chemical elements. 

The much rarer element, protactinium, was not found until 1913 when K. Fajans and O. Gohring identified Pa as an unstable member of the decay series ... 

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 most interesting elements of the seventh row are those following actinium. For some of these elements a large amount of chemistry is known. The first four, actinium, thorium, protactinium, and uranium, used to be shown in the periodic... 

An additional material based on the extractant octyl-phenyl-N,N-diisobutyl-carbamoylmethylphosphine oxide, or CMPO, (marketed under the name TRU-Spec) has also been widely utilized for separations of transuranic actinides (Horwitz et al. 1993a) but is also useful for uranium-series separations (e.g., Burnett and Yeh 1995 Luo et al. 1997 Bourdon et al. 1999 Layne and Sims 2000). This material has even greater distribution coefficients for the uranium-series elements U (>1000), Th (>10000), and Pa. As shown in Figure 1, use of this material allows for sequential separations of Ra, Th, U, and Pa from a single aliquot on a single column. Separations of protactinium using this material (Bourdon et al. 1999) provide an alternative to liquid-liquid extractions documented in Pickett et al. (1994). 

Figure 1. Schematic diagram showing a TRU-spec extraction chromatography method for separation of uranium, thorium, protactinium, and radium from a single rock aliquot. Further purification for each element is normally necessary for mass spectrometric analysis. Analysis of a single aliquot reduces sample size requirements and facilitates evaluation of uranium-series dating concordance for volcanic rocks and carbonates. For TIMS work where ionization is negatively influenced by the presence of residual extractant, inert beads are used to help remove dissolved extractant from the eluant.

Protactinium differs from all of the preceding U-series elements in that it may enter both the Ml and M2 sites. Ml is known to behave in a considerably stiffer fashion than M2 (Fig. 7 Hill et al. 2000), as befits its small size. The lack of a suite of small 5+ cations (unlike the lanthanides) makes it difficult to constrain and E by fitting a... 

Radioactive, silvery metal of which only about 125 g exists worldwide, isolated from reactor material. Protactinium occurs in the decay series of 238U (K. Fajans) as 234Pa. It also occurs in that of 235U this isotope, 231Pa, was discovered by L. Meitner and 0. Hahn. The element is only of scientific interest. 

Actinium and protactinium are so rare and expensive to make they are seldom used. Protactinium is one of the most expensive of all the elements found in nature, many times more valuable than gold. 

Meitnerium - the atomic number is 109 and the chemical symbol is Mt. The name derives from the Austrian physicist Lise Meitner , who had discovered the element, protactinium. The first synthesis of the element Meitnerium is credited to German physicists from the GSI (Center for Heavy-Ion Research) lab at Darmstadt, Germany under Gunther Miinzenberg, in 1982 using the nuclear reaction ° Bi ( Fe, n) Mt. The longest half-life associated with this unstable element is 0.07 second Mt. 

The element with 91 protons is protactinium (Pa). The isotope jPA also undergoes beta decay,... 

Protactinium is a relatively heavy, silvery-white metal that, when freshly cut, slowly oxidizes in air. AH the isotopes of protactinium and its compounds are extremely radioactive and poisonous. Proctatinium-231, the isotope with the longest half-life, is one of the scarcest and most expensive elements known. It is found in very small quantities as a decay product of uranium mixed with pitchblende, the ore of uranium. Protactiniums odd atomic number (gjPa) supports the observation that elements having odd atomic numbers are scarcer than those with even atomic numbers. 

As mentioned, protactinium is one of the rarest elements in existence. Although protactinium was isolated, studied, and identified in 1934, little is known about its chemical and physical properties since only a small amount of the metal was produced. Its major source is the fission by-product of uranium found in the ore pitchblende, and only about 350 milligrams can be extracted from each ton of high-grade uranium ore. Protactinium can also be produced by the submission of samples of throrium-230 (g Th) to radiation in nuclear reactors or particle accelerators, where one proton and one or more neutrons are added to each thorium atom, thus changing element 90 to element 91. 

It was first identified and named brevium, meaning brief, by Kasimir Fajans and O. H. Gohring in 1913 because of its extremely short half-life. In 1918 Otto Hahn (1879—1968) and Lise Meitner (1878-1968) independently discovered a new radioactive element that decayed from uranium into (actinium). Other researchers named it uranium X2. It was not until 1918 that researchers were able to identify independently more of the elements properties and declare it as the new element 91 that was then named protactinium. This is another case in which several researchers may have discovered the same element. Some references continue to give credit for protactinium s discovery to Frederich Soddy (1877—1956) and John A. Cranston (dates unknown), as well as to Hahn and Meitner. 

Periodic Table Americium, http //www.chemicalelements.com/elements/am.html (accessed September 6> 2005). Periodic Table Plutonium, http //www.chemicalelements.com/elements/pu.html (accessed September 6> 2005). Periodic Table Protactinium, http //www.chemicalelements.com/elements/pa.html (accessed September 6> 2005). Periodic Table Thorium (accessed September 6> 2005).Periodic Table Uranium (accessed September 6, 2005).Periodic Table Electron Configuration, http //www.chemicalelements.com/ show/electronconfig.html (accessed November... 

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

This article presents a general discussion of actinide metallurgy, including advanced methods such as levitation melting and chemical vapor-phase reactions. A section on purification of actinide metals by a variety of techniques is included. Finally, an element-by-element discussion is given of the most satisfactory metallurgical preparation for each individual element actinium (included for completeness even though not an actinide element), thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. 

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