Elements stars

Figure 5 A classification of the hydrides. The starred elements are the transition elements for which complex molecules or ions containing M-H bonds are known. (Ref 84. Reproduced hy permission of Wiley Inc.)...

Away from the nuclear furnaces of the stars elements can exist as the atoms we are familiar with, which in turn can form simple compounds if their concentrations are sufficiently great that atomic encounters can occur. The highest concentrations are found in interstellar clouds, and in particular in molecular clouds, where densities of 109—1012 particles per m3 can exist. This is still a very low density, and the most common constituents of these clouds are H (atomic hydrogen), H2 (molecular hydrogen) and He, which can be ionized by bombardment with high-energy particles, originating from phenomena like supernovae, and can then take part in ion—molecule reactions, such as ... 

Iron Life s Switch-Hitting All-Star Element... 

Low massive stars elements up to carbon and oxygen are produced. 

Latin carbo, charcoal) Carbon, an element of prehistoric discovery, is very widely distributed in nature. It is found in abundance in the sun, stars, comets, and atmospheres of most planets. Carbon in the form of microscopic diamonds is found in some meteorites. 

Sodium is present in fair abundance in the sun and stars. The D lines of sodium are among the most prominent in the solar spectrum. Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth s crust it is the most abundant of the alkali group of metals. 

Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Its nuclei are very stable. Iron is a principal component of a meteorite class known as siderites and is a minor constituent of the other two meteorite classes. The core of the earth — 2150 miles in radius — is thought to be largely composed of iron with about 10 percent occluded hydrogen. The metal is the fourth most abundant element, by weight that makes up the crust of the earth. 

Titanium oxide bands are prominent in the spectra of M-type stars. The element is the ninth most abundant in the crust of the earth. Titanium is almost always present in igneous rocks and in the sediments derived from them. 

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. 

Searches for the element on earth have been fruitless, and it now appears that promethium is completely missing from the earth s crust. Promethium, however, has been identified in the spectrum of the star HR465 in Andromeda. This element is being formed recently near the star s surface, for no known isotope of promethium has a half-life longer than 17.7 years. Seventeen isotopes of promethium, with atomic masses from 134 to 155 are now known. Promethium-147, with a half-life of 2.6 years, is the most generally useful. Promethium-145 is the longest lived, and has a specific activity of 940 Ci/g. 

When hydrogen is burned up in the nuclear furnace of a star, helium burning takes over, forming carbon, which in turn leads to oxygen, etc. Subsequent emission processes releasing a-particles, equilibrium processes, neutron absorption, proton capture, etc. lead to heavier elements. 

Sometimes a star explodes in a supernova cast mg debris into interstellar space This debris includes the elements formed during the life of the star and these elements find their way into new stars formed when a cloud of matter collapses in on itself Our own sun is believed to be a second generation star one formed not only from hydrogen and helium but containing the elements formed in earlier stars as well... 

Helium, plentiful in the cosmos, is a product of the nuclear fusion reactions that are the prime source of stellar energy. The other members of the hehum-group gases are thought to have been created like other heavier elements by further nuclear condensation reactions occurring at the extreme temperatures and densities found deep within stars and in supernovas. 

At the opposite end of the topological spectrum are stereocenters in terminal rings that are eligible for disconnection. Stereocenters in such rings which are elements of a retron or partial retron for a ring disconnective transform should be cleared preferentially by application of that transform. Examples 156, 157 and 158 illustrate such stereocenters (starred). 

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. 

First artificial transmutation of an element Nfa.pl gO 192S-8 First abundance data on stars (spectroscopy)... 

The following types of nuclear reactions have been proposed to account for the various types of stars and the observed abundances of the elements ... 

E. M. Burbidge, G. R. Burbidge, W. A. Fowler and F. Hoyle, Synthesis of the elements in stars. Rev. Mod. Rhys. 29, 547-650 (1957). This is the definitive review on which all later work has been based. 

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