Technetium in stars

Introduction.—The identification of technetium in stars has been confirmed, thus establishing that stellar synthesis of this element is occurring. Recent developments in the analytical chemistries of technetium and rhenium have been reviewed, as has the extraction of rhenium from hydrochloric acid solutions a text describing the analytical chemistry of technetium and other man-made elements has been published. ... 

Nucleosynthesis is the formation of elements. Hydrogen and helium were produced in the Big Bang all other elements are descended from these two, as a result of nuclear reactions taking place either in stars or in space. Some elements—among them technetium and promethium—are found in only trace amounts on Earth. Although these elements were made in stars, their short lifetimes did not allow them to survive long enough to contribute to the formation of our planet. However, nuclides that are too unstable to be found on Earth can be made by artificial techniques, and scientists have added about 2200 different nuclides to the 300 or so that occur naturally. 

Chemical elements including technetium are being produced in nuclear reactions occurring in the stars today. This has been proved by observing of the presence of technetium in some stars [1]. Technetium has no stable isotopes and none of the technetium isotopes has a half-life long enough to survive the age of the universe. So the technetium observed must have been synthesized by nuclear processes in the stars. 

Although the half-life of "Tc in steller interiors is remarkably decreased, a substantial amount of the isotope ean survive the s-process. Observations have revealed that more than 50 stars contain technetium in their outer envelope. According to other calculations, the production of neutrons in the competitive processes of neutron capture and / -decay is even more enhanced at such high temperatures, and this fact almost compensates for the depletion of "Tc [41]. 

Progress in understanding stellar evolution and nucleosynthesis, and the discovery by Merrill (1952) of the unstable element technetium in the S star R Andromedae, demonstrating the occurrence of stellar nucleosynthesis within a few half-lives of Tc (i.e. < about 1 Myr see Fig. 1.8), has led to acceptance of the idea that abundance variations among stars are perfectly natural as a consequence of three main effects (see Fig. 3.37) ... 

Almost all of the elements heavier than He are synthesized in the interiors of stars. The work of Burbidge et al. (1957) gives the theoretical framework for the synthesis of the elements. The experimental evidence of active nucleosynthesis came from the discovery of the unstable nuclei of technetium in the spectra of red giants (Merrill 1952). The solar elemental and isotopic abundances which are taken from the primitive carbonaceous chondrites constitute the guidelines for testing such models (Anders and Grevesse 1989). A minimum of eight basic processes are required to reproduce the observed compositions. Nucleosynthetic... 

McKeegan KD, Chaussidon M, Robert E (2000) Incorporation of short-lived Be in a calcium-aluminium-rich inclusion from the Allende Meteorite. Science 289 1334-1337 Merrill PW (1952) Technetium in the stars. Science 115 484-486... 

As a nuclear reaction, the s process is relatively well understood, but the problem lies in identifying an astrophysical site for it and determining the relevant physical parameters, such as neutron flux, mean time separating two neutron captures, and temperature. It has been shown that the most propitious temperatures are those of helium fusion. Added to the fact that the surfaces of certain red giants are rich in s isotopes, such as radioactive technetium and barium, this observation confirms the idea that the s process may be related to helium fusion regions in stars. 

TECHNETIUM. [CAS 7440-26-8J. Chemical element symbol Tc, at. no. 43, at. wt. 98.906, penodic table group 7, mp 2l 72 ">C, bp 4877 TT, does not occur in nature. The present location of technetium in die penodic table was vacant for many years, during which time several claims to having found the element were made, but never confirmed. One such claimant termed the element masurium. Technetium has been detected in certain stars and this discovery mnst be resolved with current theories of stellar evolution and element synthesis. 

Various theories have been advanced to explain the relative abundance of the elements. In recent years knowledge has accumulated of the types of nuclear transformations occurring in stars. A continuous process of synthesis and consumption of elements (Burbidge, Burbidge, Fowler and Hoyle, 1957) accounts for the observed differences in composition of stars of different ages and also such abnormalities as the presence of technetium in S-type stars. 

Klement 43 in the seventh subgroup of the periodic system, technetium, is the lowest atomic number radioelement. Stable, non-radioactive isotopes do not exist according to Mattauch s rule. Technetium isotopes can be produced artificially by nuclear processes. Long-lived isotopes are Tc (2.6 10 a), Tc (4.2 10 a) and Tc (2.1 10- a). The spectroscopic discovery of technetium in several fixed stars provided the first proof of stellar synthesis of heavy nuclides. Traces of Tc occur in the earth s crust where they arise mainly from spontaneous fission of... 

Ninety-one elements occur naturally on earth. Minute traces of plutonium-244 have been discovered in rocks mined in Southern California. This discovery supports the theory that heavy elements were produced during creation of the solar system. While technetium and promethium have not yet been found naturally on earth, they have been found to be present in stars. Technetium has been identified in the spectra of certain late type stars, and promethium lines have been identified in the spectra of a faintly visible star HR465 in Andromeda. Promethium must have been made near the star s surface for no known isotope of this element has a half-life longer than 17.7 years. 

The discovery of element 43, technetium, is credited to Carlo Perrier and Emilio Segr6, who artificially produced it in 1937. However, scientists have found minute traces of technetium in the Earth s crust that result from the fission of uranium. Astronomers have also discovered technetium in S-type stars. 

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. 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

In that one percent, iron, sodium, calcium, rare elements like scandium, and even elements not found on earth, like technetium, have been discovered. These elements and many others can be identified in the atmospheres of stars by spectroscopy, a method of analyzing the light emitted by our sun and other stars. Each element, whether on the earth or outside of it, always produces a certain, characteristic pattern of colored lines of light when... 

Technetium is the 76th most abundant element, but it is so rare that it is not found as a stable element on Earth. All of it is artificially produced. Even though natural technetium is so scarce that it is considered not to exist on Earth, it has been identified in the tight spectrum from stars. Using a spectroscope that produces unique tines for each element, scientists are able to view several types of stars. The resulting spectrographs indicate that technetium exists in the stars and thus the universe, but not on Earth as a stable element. 

Technetium has not been found to exist on earth. However, it has been detected in certain stars. Long-hved technetium-99 isotope of half-life 2.15x10 years is found in relatively significant quantities in fission products of uranium-235. Every Ig of uranium-235 yields about 0.027g of technetium-99 from its fission. 

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