Elements synthesis in stars

Figure 1.6 The lime-scales of the various processes of element synthesis in. stars. The curve gives the central temperature as a function of lime for a star of about one solar mass. TTie curve is schematic. ...

Thielemann RK. et al (2001) Element synthesis in stars. CERN Document server astro-ph/0101476. 

The half-life of 244Pu (8.2 X 107 years) is short compared with the age of the earth (4.5 X 109 years), and hence this nuclide is now extinct. However, the time interval (a) between the element synthesis in stars and formation of the solar system may have been comparable with the half-life of 244Pu. It has been found recently in this laboratory that various meteorites contain excess amounts of heavy xenon isotopes, which appear to be the spontaneous fission decay products of 244Pu. The value of H calculated from the experimental data range between 1 to 3 X 108 years. The process of formation of the solar system from the debris of supernova is somewhat analogous to the formation of fallout particles from a nuclear explosion. 

Second, an element must be soluble in water to be available for life. The concentration of the chemical elements in sea water may give us the result of both effects, elemental synthesis in stars and release from the Earth s crust into water (Table 1.1). Table 1.1 also provides information (enrichment E) if a given element has been enriched (or to the contrary) on its way from ancient stars to our sea water and from the Earth s crust to sea water. The term is expressed as the decadic logarithm thus, for example, lg(E) = 2 means a 100-fold enrichment, and lg(E) = — 2 a 100-fold impoverishment. Since the abundance of an element in the universe is compared to that of hydrogen, lg(E) = 0 for H in Table 1.1. 

Balick (1975) computes the ionization structure of H, N, 0, Ne and S for various kinds of frequency dependence of dust absorption and for variable dust-to-gas ratio. However, while the dust-to-gas mass ratio varies from 10 to 10 the element abundance stays constant. In a subsequent paper Balick and Sneden (1976) consider the effect of variable heavy element abundances Z in both HII region and ionizing star but now the effect of dust is neglected and the mass fraction of He is kept constant. In a more realistic model both the dust-to-gas ratio and that part of the He-abundance AY(He) which results from element synthesis in stars should vary proportionally to Z. The most recent model calculations by Mathis (priv. comm.) allow the variation and combination of all these parameters. 

Fowler, W.A., Burbidge, G.R. Burbidge, E.M. 1955 Nuclear reactions and element synthesis in the surfaces of stars. ApJS 2, 167. 

In stars the size of our own Sun, however, such reactions are unlikely to occur, and the production of carbon and oxygen mark the final stage of heavy element synthesis in such stars. 

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. 

The origin of chemical elements has been explained by various nuclear synthesis routes, such as hydrogen or helium burning, and a-, e-, s-, r-, p- and x-processes. "Tc is believed to be synthesized by the s (slow)-process in stars. This process involves successive neutron capture and / decay at relatively low neutron densities neutron capture rates in this process are slow as compared to /1-decay rates. The nuclides near the -stability line are formed from the iron group to bismuth. 

Table 2.2 lists the most important syntheses occurring in the stars. The main products include the bioelements C, O, N and S. The synthesis of the elements began in the initial phase after the big bang, with that of the proton and the helium nucleus. These continue to be formed in the further development of the stars. The stable nuclide 4He was the starting material for subsequent nuclear syntheses. Carbon-12 can be formed in a triple a-process, i.e., one in which three helium... 

Further capture of a-particles leads to the formation of oxygen and neon. 160 itself forms the basis for the synthesis of sulphur. The only biogenic element missing in Table 2.2 is phosphorus, which is an exception in that it is formed by a complex nuclear synthesis (Macia et al., 1997). In large stars, the reactions listed in the table take place in the following series, without stopping but over long periods of time. 

Large-scale production of the heavier nuclei requires a heavier initial mass than that of the Sun. All nuclei up to iron were formed in stars with about 20 solar masses, as summarised in Table 4.2, which shows the important role of heavier stars in the cosmic nuclear synthesis of heavier elements. 

Burbidge EM, Burbidge GR, Fowler WA, Hoyle F (1957) Synthesis of the elements in stars. Rev Mod Phys 29 547-630... 

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. ... 

Pu may be considered as an ideal tracer nuclide for these studies because of its decay characteristics. Its existence or absence in the early solar system can be considered as a crucial test for or against the theories of the synthesis of chemical elements in stars. 

The remainder of the Fowler article is of great interest, but in detail that is beyond the scope of this encyclopedia. Topics covered by Fowler include early research on element synthesis stellar reaction rates from laboratory cross sections hydrogen burning in main-sequence stars and the solar neutrino problem synthesis of l3C and, 60 and... 

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. 

Wallerstein, G., Iben, I. Jr., Parker, P. et al. (1997) Synthesis of the elements in stars forty years of progress. Reviews... 

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. 

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