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A historical account of element 43 is presented in this paper in four main phases: (a) the many searches and claims prior to its actual discovery in 1937; (6) its discovery and the preparation and identification of its isotopes; (c) its discovery in stars, and the theories to explain its presence there; and (d) the recent searches for naturally occurring terrestrial technetium. The chemistry of technetium is not treated here since it is more than adequately discussed by Anders (1) and Boyd (2).In his periodic table, Mendeleev (3, 4) left certain gaps and predicted that new elements would be discovered in time to fill these gaps. The atomic weights and physical, and chemical properties also were forseen.Two of these "missing" elements were congeners of manganese, which we know today as technetium and rhenium, elements 43 and 75. Because thenproperties would seem to be similar to manganese, he named them tentatively eka-manganese and dwi-manganese (sometimes written dvi-manganese), with the symbols Em and Dm. Their atomic weights were predicted to be 100 and 190, respectively. Further predictions were that their compounds would be colored and there would be a series of oxides corresponding to the oxides of manganese.The periodic table has provided a blueprint which indicated how many elements were possible up to the heaviest natural element, uranium. By about the middle of the third decade of this century, all 92 elements had been discovered, with the exceptions of elements 43, 61, 85, and 87. Even these found their way into the periodic table under various names.However, these "discoveries" were erroneous and, in the 1930's, it could be shown that these elements are all radioactive, having such short half-lives that their existence in appreciable amounts on the earth is not possible (5).Early Attempts To IsolatePolinium: The first recorded claim of finding a new element which would correspond to element 43 was in 1828.Osann, (6) while studying platinum ores, claimed three new elements, among which was one he named polinium. However, he later reported that polinium was actually impure iridium (7).Ilmenium: While examining various minerals, Hermann (8), in 1846, found what was thought to be a newThis paper is based on a portion of the dissertation submitted by the author to the Graduate School of the University of Arkansas in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

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The use of selenium in stainless steels and the importance of selenium in biological materials and processes have been discussed in the literature (1-6). However, the separation and determination of selenium in these materials by conventional chemical methods can be difficult, tedious, and, if care is not exercised, subject to inaccuracies due to volatilization (1, 4-10). Neutron activation analysis techniques also have been used for the determination of selenium (2, 5). Generally, the production of 120-day 78Se, 17.4-second 77™Se, and 18.6-minute 81sSe has been used for the analysis (2). However, with selective dry distillation techniques, standard radiochemical procedures are not required and quantitative recovery is possible. The radiochemistry of selenium has been discussed by Leddicotte (11) and DeVoe (12).In the method reported here, the selenium-containing sample and a standard are irradiated by either thermal neutrons or by 14-MeV neutrons. The selenium is then separated by a dry distillation technique and is determined by counting the gamma rays of 121-day 75Se or 57-minute 81"'Se. This method also permits the qualitative identification of selenium by the appearance of the metal in the dry distillation collection tube. The various known neutron reactions which can occur are given elsewhere (13-15). EXPERIMENTAL Apparatus and Reagents. The counting system included a 3-X 3-inch Nal(Tl) crystal, with associated electronics, connected to a Technical Measurements Corp. 400-channel analyzer.Thermal neutron irradiations of samples were performed in the Sandia Reactor Facility (SRF) in a position which had

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