Artificial elements production

Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

Promethium is a silvery-white, radioactive metal that is recovered as a by-product of uranium fission. Promethium-147 is the only isotope generally available for smdy. The spectral lines of promethium can be observed in the light from a distant star in the constellation Andromeda. Even so, it is not found naturally on Earth, and scientists consider it to be an artificial element. Its melting point is 1,042°C, its boiling point is estimated at 3,000°C, and its density is 7.3 g/cm. ... 

Taken together, these papers provide insights on the structure and cognitive content of twentieth century chemistry. They all deserve careful reading and, rather than trying to summarize them, I have organized my presentation around a number of salient issues which relate them to one another the value and status of physical evidence in chemical disciplines the relationship between the identification of an element and its production the contrast between natural and artificial elements and the disciplinary dynamics that attended all of these changes. 

Activation Production of radionuclides by nuclear reactions Artificial elements Man-made elements produced by nuclear reactions Autoradiography Picture produced by nuclear radiation in photographic films or plates... 

Technetium is an artificial element, available as Tc (a P-particle emitter, fi = 2.13 x 10 yr) which is isolated from fission product wastes by oxidation to [Tc04]. Separation... 

In recent years, the number of elements has increased well beyond 100 as the result of the synthesis of artificial elements. At the time of writing, conclusive evidence has been reported for element 111. Such elements are typically very unstable, and only a few atoms are produced at any time. However, ingenious chemical techniques have been devised that permit the chemical properties of these so-called superheavy elements to be examined and allow one to check whether extrapolations of chemical properties are maintained for such highly massive atoms. On a more philosophical note, the production of these elements allows us to examine whether the periodic law is an exceptionless law, of the same kind as Newton s law of gravitation, or whether deviations to the expected recurrences in chemical properties might take place once a sufficiently high atomic number is reached. No surprises have been found so far, but the question of whether some of these superheavy elements have the expected chemical properties is far from being fully resolved. One important complication that arises in... 

All the artificial elements are, of course, radioactive, and the first to be prepared was technetium. It was produced in vanishingly small quantity in 1939 by Segre and Perrier by bombarding element 42 (molybdenum) with deuterons for several months. It was also detected the following year among uranium fission products. A few years later, the same source yielded promethium, the missing rare earth element. 

Atoms with the same value of Zbut different values of A are isotopes (Table 11.1). Many isotopes are stable but others are naturally or artificially radioactive, i.e. their atomic nuclei disintegrate, emitting particles or radiation. This changes the nuclear structure of the atom and often results in the production of a different element. 

The following is a procedure recommended for elucidating the structure of complex organic molecules. It uses a combination of different NMR and other spectroscopic techniques. It assumes that the molecular formula has been deduced from elemental analysis or high-resolution mass spectrometry. Computer-based automated or interactive versions of similar approaches have also been devised for structural elucidation of complex natural products, such as SESAMI (systematic elucidation of structures by using artificial machine intelligence), but there is no substitute for the hard work, experience, and intuition of the chemist. 

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