Elements Heavier than He

The gas disperses and the interstellar matter becomes enriched with heavier elements. 

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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... 

The fate of stars also depends on the presence of a companion. Other violent episodes known as Novae or type la supemovae result from the accretion of materials from a partner star. Supemovae of type I are thought to be responsible for most of the production of the neutron-rich isotopes of the iron group (Woosley et al. 1995 Hoflich et al. 1998). One of the key parameters in stellar evolution, and consequently the nucleosynthetic outcome, is the metallicity, defined as the proportion of elements heavier than He. 

Settling or diffusion of heavy elements from the photosphere to the interior boundary layer of the convection zone and beyond lowered the elemental abundances (relative to H) from protosolar values 4.56 Gyr ago (see [30]). Over the Sun s lifetime, diffusion decreased abundances of elements heavier than He by 13% from original protosolar values, whereas that of He dropped a little more by about 15% modeling these depletions also depends on opacities, hence abundances. With these estimates, the proto-solar abundances (subscript 0) are calculated from the present-day data for the astronomical scales as... 

Uranus and Neptune are smaller and denser than Jupiter and Saturn due to much larger enrichments of elements heavier than He. Oxygen is highly enriched on these planets and the net thermochemical reaction... 

The space between stars is not empty but filled with a gas and dust component that is called the interstellar medium. Stars are bom out of interstellar clouds and at the end of their evolution they enrich the interstellar medium with elements heavier than He. Depending on their masses, stars become either unstable emitting strong stellar winds or expelling their outer atmosphere, the more massive stars explode and become a supernova. 

Astrophysicists call aU elements heavier than He metals. 

The majority of the Universe is made from hydrogen and helium produced during the Big Bang, although some He has been made subsequently. The relative cosmic abundance of some of the elements relevant to the formation of life is given in Table 1.2, with all elements heavier than H, He and Li made as a result of fusion processes within stars, as we shall see later. The cosmic abundance is assumed to be the same as the composition of the Sun. 

The cosmic abundance of elements forms a basis for considering the chemical composition of ice in space. The cosmic abundance of major elements is summarized in Table 9.1. The most abundant elements, H and He, are veiy volatile, and exist as gas in the tenuous environment in space. Elements heavier than H and He can form solids. The elements C, N, and O combine with H to form ices at temperatures lower than about 100K, and Si, Mg, and Fe combine with O to form silicates, metals, and their oxides. Note that the elements that form ices are much more abundant than tlie elements that form silicates and metals. 

He was a member of the faculty in the department of physics at Berkeley as an instructor in 1935, an assistant professor in 1936 and 1941, and a professor in 1946. In 1940 the creation of element 93, neptunium (symbol Np), was announced by Edwin M. McMillan and Philip H. Abelson. It was the first element heavier than uranium (known as a transuranium element). 

Glenn T. Seaborg, Nobel Laureate chemist and Chancellor of the University of California at Berkeley, is the co-discoverer of nine of the 102 chemical elements. He is the only man since Dmitri Mendeleev to have made a major change in the Periodic Table of the Elements—a change which led immediately to the discovery of the first element heavier than plutonium and subsequently to the discovery of another half dozen transuranium elements. 

Abelson, Philip Ha use (1913-2004) American physical chemist who developed a massive gas diffusion apparatus for the separation of the fissionable uranium-235 isotope from the natural mixture, which was almost all uranium-238. This was an early stage in the production of the first atomic bomb. Abelson also assisted in the creation of the manufactured element neptunium, the first element heavier than uranium. Later he worked with Stanley Miller to try to show in the laboratory how life might have originated on Earth. 

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