Protactinium physical properties

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. 

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. 

He was one of the first to conclude in 1912 that some elements can exist in forms that are chemically identical, and save only as regards the relatively few physical properties which depend on atomic mass directly, physically identical also. He called them isotopes. Later he promoted their use in determining geologic age. He is credited (with others) with the discovery of the element protactinium in 1917. 

Protactinium see also Elements electrical resistivity, 12-39 to 40 electron configuration, 1-18 to 19 heat capacity, 4-135 history, occurrence, uses, 4-1 to 42 ionization energy, 10-203 to 205 isotopes and their properties, 11-56 to 253 magnetic susceptibility, 4-142 to 147 physical properties, 4-133 to 134 thermal properties, 12-201 to 202 vapor pressure, high temperature, 4-136 to 137... 

It had long been known that the chemical properties of thoridm, protactinium and uranium resemble those of the 4d and 5d elements. For this reason most of the textbooks and standard works on chemistry and physics in which the electronic structure was discussed accepted the view that it was the 6d shell that was being filled. 

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